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ILLINOIS 
STATE  GEOLOGICAL  SURVEY. 


/U^  /5^w^ 


BULLETIN  No.  9. 


Paving  Brick  and  Paving  Brick 
Clays  of  Illinois. 


BY 


C.  W.  ROLFE,  R.  C.  PURDY,  A.  N.  TALBOT 
AND  I.  O.  BAKER. 


Urbana 

University  of  Illinois 

1908 


SPRINGFIELD,  ILL. 

Illinois  State  Journal  Co.,  State  Printers 

1908 


STATE  GEOLOGICAL  COMMISSION. 


Governor  C.  S.  Deneen,  Chairman. 
Professor  T.  C.  Chamberlin,  Vice  Chairman. 
President  Edmund  J.  James,  Secretary. 


H.  Foster  Bain,  Director. 

C.  W.  Rolfe,  Consulting  Geologist  in  the  Investigation  of  Clays. 


Digitized  by  the  Internet  Archive 

in  2012  with  funding  from 

University  of  Illinois  Urbana-Champaign 


http://archive.org/details/pavingbrickpavin09rolf 


CONTENTS. 


Page 

List    of    Illustrations     v 

Letter    of    Transmittal     J) 

Geology  of  Clays ;  by  C.  W.  Rolf e  ' .' [ 

Introduction    -, 

Elementary    Chemical    Principles     \ 

Silica  and   Silicic   Acid    

Formation    of    Silicates     .  \\\ 3 

Chemical  and  Mineralogical  Composition  of  Granitoid   Rocks 

Principal  Minerals  which  occur  in  several  groups  of  Crystalline  Rocks 

Chemical  Composition   of   Crystalline   Rocks 5 

Table    of   Minerals    Common    in    Crystalline    Rocks,    with    the    Chemical 

Composition    of    each     5 

Table  showing  percentages  of  the  More  Common  Elements  in  the  Sur- 
face  Layers   of*  the   Earth    - 

Original  Composition  of  the   Earth's   Crust    ... 7 

Decomposition   of  Granitoid  Rocks s 

General  Agents  and  Progress    ...'. 8 

Formation    of   Residual   Clays 10 

Origin   of   Impurities    Occurring   in   Clays 11 

Analyses   of    Typical    Clays    [ 23 

Percentages   of   Clay   Substances 14 

Agents   which  Aid  in  Decomposition  of  Rocks 15 

Depth  of  Deposits  of  Residual  Clays    16 

Formation  of  Sedimentary  Rocks  and  Clays 16 

Erosion   and    Transportation 16 

Transported    Clays    '.'.'.'.'.  17 

Comparison  of  Residual  and  Transported   Clays .... . ........ 17 

Re-Erosion,   Transportation   and   Final   Deposition   of   Clays 18 

Formation    of   Shales    18 

Changes    in   Sedimentary   Rocks 19 

Emergence   of    Sedimentary   Rocks 19 

Metamorphism    of    Sedimentary    Rocks    and    Formation    of   Deposits    of 

Residual    Clays    90 

Decomposition    of    Sedimentary    Rocks    and    Formation    of    Deposits"  of 

Residual    Clays    21 

The    Special   Action   of  Ice 22 

Ice  as  an  Eroding  and  Transporting  Agent 22 

Ice  as  an  Agent  of  Deposition    23 

Characteristics    of   Glacial    Clays    24 

Origin    of   Loess    25 

Classification    of   Clays    26 

Kaolin      26 

Ball    Clays 27 

Fire    Clays     9g 

Flint     Clays     31 

Pottery    Clays    , 32 

Vitrifying   Clays    32 

Terra-cotta    Clays    33 

Brick    Clays    , 34 

Drain   Tile    Clays    34 

Gumbo    Clays    34 

Loess   and  Abode    Clays    35 

Fullers    Earth    35 

Minor  Uses   for   Clays    35 


VI 

Contents — Continued. 

Page 

Geological  Distribution  of  Paving  Brick  Materials  in  Illinois;  by  C.  W.  Rolfe...  36 

Introduction     36 

What    is'  Paving    Brick? 36 

What    is    Paving    Brick    Clay? 36 

What    is   Vitrification?    37 

Distinction    between    Vitrification    and    Fusion 38 

Conditions  Essential   in   a   Paving  Brick   Clay 38 

Geology    of    Clays    40 

Origin 40 

Outline  of  the  Geological  History  of  Illinois 40 

General    section    40 

Cambrian 41 

Potsdam    41 

Ordovician.    41 

Lower   Magnesian    41 

St.    Peters    41 

Galena-Trenton     42 

Cincinnatian    or    Maquoketa     42 

Silurian     42 

Niagaran     42 

Devonian      42 

Carboniferous     ; 43 

Mississippian    or    Lower    Carboniferous     43 

Fennsylvanian    or    Coal    Measures     43 

Cretaceous    and    Tertiary     43 

Pleistocene     43 

Glacial   Deposits    43 

Areal    Distribution     44 

Ordovician     44 

Silurian 45 

Devonian 45 

Mississippian    or    Lower   Carboniferous 45 

Pennsylvanian  .or   Coal   Measures    45 

Cretaceous    and    Tertiary    4(! 

Qualities  of  High  Grade  Paving  Brick  and  Tests  Used   in  Determining  Them; 

By   A.    N.    Talbot    47 

Introduction      47 

Qualities   of  High  Grade   Paving  Brick    48 

General     48 

Toughness,    Hardness    and    Strength     49 

Uniformity    of    Quality     50 

Homogeneity  of  Structure  and  Freedom  from  Lamination   50 

Weather-Resisting    Quality     .  .• 50 

Regularity    of    Form    and    Size    51 

Tests   for   Quality    51 

General    Statement    51 

Rattler    Test 52 

Original  Specifications:  Old  N.  B.  M.  A.  Test   55 

National  Brick  Makers   Standard   Rattler  Test    58 

Talbot-Jones  Rattler  Test   59 

Absorotion    Test 60 

Crushing    Test     62 

Cross-Breaking     Test     62 

Specific    Gravity     64 

Discussion  of  Tests  and  Comparison  of  Qualities  of  Brick  Tested  64 

Requirements  for  Paving  Brick   69 

Inspection    of    Paving    Brick     70 

Tests    for    Paving   Brick    71 

General    Statement    71 

Rattler    Tests     75 

Transverse,   Absorption   and   Crushing   Tests    81 

Qualities  of  Clays  Suitable  for  Making  Paving  Brick;  By  Ross  C.   Purdy 133 

Introduction    133 

Nature   of   the    Problems   Involved    133 

Physical     Properties     136 

Introduction 136 

Specific    Gravity     136 

Real  and  Apparent   Specific   Gravities    136 

Methods    of    Determination     136 

Determination    by    Seger   Volumeter    136 

Determination    by    Pycnometer 138 

Determination   with   Chemical   Balance    138 

Porosity     140 

Definition     140 

Methods    of    Determination     140 

First    Method — Volumeter    141 

Second   Method — Chemical    Balance    141 

Third    Method— Calculation     142 


VII 

Contents — Continued. 

Page 
Qualities  of  Clays  Suitable  for  Making  Paving  Brick;  By  Ross  C.  Purely— Concluded. 

Relation  of  Rate  of  Absorption  to  Porosity  14r 

Value  of  Porosity  Determination   on   U  iw  Clay                          ,    - 

Value  of  Porosity  Determination  on   Green   Brick                     ilc 

Fineness   of  Grain    j™ 

Definition Ho 

Means    of    Expressing 149 

Value    of    Determination |^y 

Numerical    Results jci 

Shrinkage   in   Drying    /    '                   |^ 

Methods    of    Measurement \?\ 

Relation   of  Volume   Shrinkage  to   Porosity     {« 

Relation   of  Volume   Shrinkage   to   Water  of   Plasticity \tt 

Relation  of  Volume  Shrinkage  to  Water  in  Excess  of  that  required 
to   fill  the  pores 


Relation  of  Volume  Shrinkage  to  fineness  of  grain 


&r~::::\\r:::*:.::.:  ..:::::::::::::  i]] 

Methods   of    Testing    \b* 

Fox    Method    .'.'.' J™ 

Wedging  Versus   Slio   Process    '  {^ 

Effect    of   Fine    Grinding    jx* 

Results    of    Tests     .' '  }™j 

Relation  of  Tensile  Strength  to  Fineness  of  Grain 170 

Relation  of  Tensile  Strength  to  Volume  Shrinkage       "  179 

Plasticity    ■ ^ ' - 

Theories    of    Plasticity    ".'.'. ±Li 

Molecular   Attraction    Theory    170 

Size   of  Grain   Theory    (iq 

Plate    Structure    Theory    U« 

Pectoidal    Theory     |J2 

Adsorption    Theory     j™ 

Development    of   Plasticity    in   Presence    of   Water"  '    iso 

Gravity     ; 1°-' 

Molecular    Attraction     -,%% 

Surface     Tension     '. Jq^ 

Surface    Pressure iq« 

Solutions    Causing   Deflocculation '   19V 

Solutions  Causing  Flocculation    '    104 

Summary     "  ' -^ 

Supposed    History    of    the    Development    of    Plasticity  "in"  Clavs"  in     ' 

Nature     J  195 

Methods    of    Measuring    Plasticitv 107 

General "  "  1 Q7 

Shape   of  the  Test  Piece    \Vo 

The    Clips     '.""".' 198 

Manufacture    of    Briquettes    '.'.'. '   190 

Adjustment    and    Calibration     ' 190 

Method    of    Procedure    '   1  q« 

Plasticity     Modulus     ".'"".".' {99 

Chemical  Properties   of  Clays '    9qq 

Value   of   Chemical  Analyses    '  '  '   900 

Mineralogical    Composition    of    Clays    \\\ 993 

Complexity  of  Mineralogical  Composition  of  Clay ?04 

Ultimate    Chemical    Composition    9Q6 

Pyro-Physical   and    Chemical    Properties    of    Paving   Brick    ciays; '*By    Ross "c 

Purdy     217 

Introduction    "   91 7 

Relations 917 

Relative  Importance  of   "Raw"   and    "Burning"   Properties ">19 

Dehydration ' '  29o 

Nature    of   Process 990 

Loss  Due  to   Constituents  Other   than   Water    221 

Oxidation     "  "   922 

General    Conditions 999 

Definition    of     Terms 222 

Evidence  of  Oxidation  in   "Raw"   Clav 223 

Oxidation  of  Clay  in  Burning   * "   223 

Substances   that  are  Affected    '. 223 

Carbon   and    Carbon    Compounds 224 

Ferrous    Carbonate 224 

Ferrous    Sulphide 226 

Other    Substances 227 


VIII 

Contents — Continued. 

Page 
Pyro- Physical  and  Chemical  Properties  of  Paving  Brick  Clays;  By  Ross  C.  Purdy—  Concluded. 

Effect  of  Chemical  and  Physical  Properties    227 

Varied   Distribution   of   Carbon    227 

Fineness   of  Grain    228 

Stable    Iron    Compounds    228 

Structure    of    Clay    Ware    229 

Temperature  as  a  Factor  in  Oxidation   230 

Moisture  as  a  Factor  in  Delaying-  Oxidation   230 

Physical  and  Chemical  Effects  of  Incomnlete   Oxidation    230 

Usual    Effects     230 

Exceptional     Effects     231 

Fusion      : 232 

Fusion    Period    of    Clays    232 

Factors    Affecting    Rate    of    Fusion    233 

Mineralogical    Composition    233 

Size    of    Grain    235 

Volatile    Matter    237 

Structure    of    Ware     238 

Material      238 

Summary     239 

Relation  of  Chemical  and   Physical  Constitution  to  Behavior   in  Fusion  239 

Chemical    Composition     239 

Historical      239 

Effect  of  Alo03  in  Ceramic  Mixtures    240 

Effect  of   Silica  in  Ceramic  Mixtures    241 

Effect  of  Magnesium  Oxide   in   Ceramic  Mixtures    243 

Effect  of  Calcium   Oxide   in   Ceramic  Mixtures    244 

Effect  of  Other  Oxides  in  Ceramic  Mixtures   247 

Influence  of  Size  of  Grain  on  the  Fusion  of  Clays   247 

Direct   Evidence    247 

General   Analysis   of  Results    248 

Thermo-Chemical  and  Physical  Changes  During  Fusion   250 

Notes  on  the  Microscopic   Structure  of  Certain   Paving  Brick  Clays 

at  Various  Stages  of  Fusion;   (By  Carroll  H.  Wegemann)    254 

General    Structure    254 

Description    of    Slides    254 

Summary  of  Changes  Observed    256 

Specific   Gravity,   Volume   and   Porosity   Changes   of   Clays    Studied; 

(By   R.    C.    Purdy)    257 

Differentiation  between   Clays   on  a   Basis  of  Rate  and  Manner  of  De- 
crease in  Porosity  and   Specific  Gravity    259 

Introduction     259 

Importance    of    Slow    Vitrification     259 

Preliminary    Trials    259 

Manufacture  of  Test  Cones    259 

Setting  Test  Pieces   After  Drying    259 

Burning     260 

Testing    of    Trial    Pieces    260 

Difficulties    Encountered    260 

Data    Obtained    262 

Summary    263 

Final    Trials     264 

Wedging     264 

Moulding     264 

Marking     3o4 

Drying     264 

Firing1     ^o4 

Cooling     •  v  •  *  •' m  •;•. 265 

Preparation  of  Briquettes  for  Testing  265 

Drying     266 

Saturation    of    Briquettes    266 

Calculations     267 

Plotting    of    Results    267 

Data    Obtained 267 

Summary    of    Results    of    Tests 270 

Number  One  Fire  Clays   270 

Number  Two  Fire   Clays    272 

Number    Three    Fire    Clays    272 

Fire    Clays    in    General    273 

Building  and  Paving  Brick  Clays   274 

Clay? Tested  Which1  are  Suitable  'for  Use  in  "the  Manufacture  of  Paving  Brick; 

Compiled  by  C.   W.   Rolfe    279 

Introduction •. $'* 

Description    of    Deposits    £»" 

Chemical    Analyses     £** 

Rational    Analyses     £°£ 

Physical    Tests    - ^ 


A 


IX 

Contents — Concluded. 


Page 

Construction  and  Care  of  Brick  Pavements;  By  Ira  O.  Baker  289 

Introduction    289 

Historical     289 

Width    of    Pavement    290 

Construction    of    Subgrade    291 

Foundation 292 

Choice    of    Materials     292 

Concrete     293 

Gravel 295 

Broken    Stone    296 

Brick     296 

Cushion     297 

Brick     298 

Character     298 

Testing 298 

Setting  the  Brick 299 

Inspection     299 

Rolling    the    Pavement    299 

Filling  the  Joints    t 300 

Sand    Filler     300 

Tar     Filler     ■ 300 

Cement    Filler    301 

Merits    of    Brick    Pavements    303 

Index     305 


LIST  OF  ILLUSTRATIONS. 


PLATES. 


Plate  1. 


Plate  2. 
Plate  3. 


Fig. 
Fig. 
Fig. 
Fig. 
Fig. 


Fig.     6. 

Fig.     7. 

Fig.     8. 

Fig.     9. 

Fig.  10. 

Fig.  11. 

Fig.  12. 
Fig.  13. 
Fig.  14. 

Fig.  15. 

Fig.  16. 
Fig.  17. 
Fig.  18. 

Fig.  19. 

Fig.  20. 

Fig.  21. 

Fig.  22. 

Fig.  23. 

Fig.  24. 

Fig.  25. 

Fig.  26. 

Fig.  27. 

Fig.  28. 

Fig.  29. 

Fig.  30. 

Fig.  31. 

Fig.  32. 

Fig.  33. 


Page 

Brick  which  underwent  normal  changes  in  density,  specific  gravity 
and   shrinkage,    in    spite    of   blackening-   due    to    imperfect    oxidation 

The*  'TaYbot- Jones'  Rattler' '.'.'.'.'.'.'.'.'.'.'.'.'.'.'.'.'.'.' .'.V.' .■.'.';;.'.'.'.'.':. .  .^^l!^! 
Brick  being  tested   for   cross-breaking  strength    63 

FIGURES. 

Rate  of  absorption  of  paving  brick    60 

Arrangement   for   testing   cross-breaking   strength   of   brick    63 

Results   of  tests   of  paving  brick    66 

Curve  showing  relation  between  porosity  and  fineness  of  grain   ......   146 

Diagram   showing  the  relation   between  porosity  of  green   shale   brick 

and  the  absolute   fineness   of  grain    147 

Kennedy  curves  showing  the  relative  rates  of  loss  on  heating  cal- 
careous   and    non-calcareous    clays.      (After    Bleininger.    Geol.    Sur. 

Ohio,   4th  Ser.  Bull.  4.   p.   179)    153 

Diagram  showing  relation  between  volume  shrinkage  and  porosity   of 

dried  brick.     (From  data  in  Tables  I.)    156 

Diagram    showing    relation    between    volume    shrinkage    and    porosity 

of  loess  clays  from  Iowa.     (After  Beyer  and  Williams.)    157 

Diagram    showing    relation    between    amount    of    water    required    to 

develop   plasticity  and  volume   shrinkage    159 

Diagram    showing   relation    of   volume    shrinkage    to    water    in    excess 

of  that  required  to  fill  the  pores  in  Iowa  clays    160 

Diagram  showing  relation  of  volume  shrinkage  to  water  in  excess  of 

that  required  to  fill  the  pores  in  Illinois  clays  161 

Diagram  showing  relation  of  volume  shrinkage  to  fineness  of  grain..   162 

Krehbiel   device   for   grooving   briquettes    164 

Diagram   showing   relation    between   tensile    strength    and    fineness    of 

grain     170 

Diagram    showing    relation    between    volume    shrinkage    and    tensile 

strength    172 

Diagram  showing  operation  of  forces  causing  surface  pressure   190 

Diagram   showing  operation  of  forces   causing  surface  tension    191 

Diagram   showing  operation   of  fluxes  in  kaolin,   using  equal  parts   of 

each     207 

Diagram    showing    operation    of    fluxes    of   kaolin,    using    fractions    of 

their  atomic   weights    '. 208 

Diagram    showing    operation    of    fluxes    on    Silica-Alumina    mixtures 

using   equal    weights    of    each    ,. 209 

Diagram    showing    the    results    of    Richter's    investigation    of    various 

oxides     210 

Seger's    Si02  —  A1203    curve     212 

Melting  points  of  mixtures  of  magnesite  and  kaolin.     (After  Rieke.)..   213 

Mellor's    fusion   curve    for   flint-feldspar   mixtures    214 

Physical    alterations    produced   by    burning    compared    with    unburned 

condition    of    clay     232 

Curves  showing  physical  changes  in  clay  at  various  stages  of  burning  257 
Curves  showing  physical  changes  in  clay  at  various  stages  of  burning  258 

Kiln  used   in   burning  experiments    261 

Decrease  in  porosity  with  burning  in  terms  of  cones 262 

Differentiation  of  Are  clays  on  basis  of  porosity  changes    271 

Curves  showing  changes  in  specific  gravity  of  fire  clays  with  pro- 
gressive  intensity   of   heat  treatment    272 

Curves    showing    changes    in    porosity    of   paving    and    building    brick 

clays  with  progressive  intensity  of  heat  treatment   275 

Curve    showing    changes    in    specific    gravity    of    paving   and    building 

brick  clays  with  progressive  intensity  of  heat  treatment   276 


X 


LETTER  OF  TRANSMITTAL. 


State  Geological  Survey, 

University  of  Illinois, 

Urbana,  May  1,  1908. 

Governor  C.  S.  Deneen,  Chairman,  and  Members  of  the  Geological  Com- 
mission : 

Gentlemen — I  submit  herewith  for  publication  as  Bulletin  9  of 
this  Survey  a  report  upon  the  Paving  Brick  and  Paving  Brick  Clays 
of  the  State,  prepared  under  the  direction  of  Professor  Rolfe  and  written 
by  Messrs.  Rolfe,  Purdy,  Talbot  and  Baker.  This  report  has  been  pre- 
pared in  cooperation,  especially,  with  the  Department  of  Ceramics  of  the 
University.  The  work  was  begun  in  1906,  but  owing  to  various  causes, 
particularly  the  desire  to  make  it  complete  and  conclusive,  its  comple- 
tion has  been  delayed  to  this  time.  When  the  investigation  began  it  was 
found  necessary  to  take  up  first  of  all  the  study  of  the  qualities  in 
clays  which  permit  their  manufacture  into  satisfactory  pavers,  and  the 
means  of  determining  those  qualities.  The  numerous  excellent  studies 
made  by  other  states  and  by  individuals,  while  clearing  up  many  of  the 
difficulties,  had  proved  to  a  considerable  extent  inconclusive,  and,  as  de- 
tailed in  this  report,  there  was  no  existing  method  of  determining  in 
advance  of  actual  trial  on  a  working  scale,  the  adaptability  of  a  clay  to 
this  purpose.  Before  we  could  test  our  clays  it  was  clearly  necessary 
to  make  a  study  of  the  methods  of  testing.  In  order  to  eliminate  the 
possible  effect  of  local  peculiarities,  it  was  determined  to  base  this  pre- 
liminary study  upon  the  best  known  paving  brick  clays  of  neighboring 
states,  as  well  as  of  Illinois.  The  active  cooperation  of  Edward  Orton 
then  State  Geologist  of  Ohio,  State  Geologist  W.  S.  Blatchley  of  Indiana, 
Dr.  E.  M.  Shepard  of  Missouri,  and  of  State  Geologist  E.  Haworth  of 
Kansas,  made  this  possible.  It  is  regretted  that,  owing  to  various 
causes,  it  was  impossible  to  secure  samples  from  the  Iowa  plants  at  the 
time. 

Profesor  C.  W.  Eolfe,  Consulting  Geologist  of  the  Survey,  and 
Director  of  the  courses  in  Ceramics  of  the  University,  lias  been  in  gen- 
eral charge  of  the  work,  and  has  prepared  the  chapters  on  the  "Geology 
of  Clays,"  the  "Geological  Distribution  of  Paving  Brick  Material  in 
Illinois,"  and  on  "Clays  Tested.  Which  are  Suitable  for  Use  in  the 
Manufacture  of  Paving  Brick."  In  the  case  of  the  latter,  he  is  responsi- 
ble for  the  form  only,  having  compiled  the  subject  matter  from  the  field 
and  laboratory  notes  of  the  various  members  of  the  Survey,  in  order  to 

XI 


XII 

secure  a  convenient  and  uniform  presentation  of  results.  The  field  col- 
lections were  made  by  the  following  individuals,  the  samples  collected 
by  them  being  indicated  by  the  accompanying  initial: 

Mr.  J.  F.  Krehbiel,  K  1-14. 

Mr.  H.  B.  Fox,  F  1. 

Mr.  E.  T.  Hancock,  H  16,  17,  18,  20,  21,  23. 

Mr.  F.  H.  Ridell,  R  1-3. 

Mr.  E.  M.  Shepard,  S  1-2. 

Mr.  Frank  P.  Brock,  L,  B,  H  2. 

Mr.  Fred  J.  Cambern,  G.  I. 

The  special  laboratory  investigations  of  the  clays  themselves,  together 
with  the  rattler  tests  of  the  brick,  were  carried  out  by  or  under  the  direc- 
tion of  Mr.  Eoss  C.  Purdy,  then  Instructor  in  Ceramics  in  the  University 
of  Illinois,  and  now  associate  Professor  in  Ceramics  at  Ohio  State 
University.  Mr.  Purdy  had  the  assistance  of  Messrs.  J.  F.  Krehbiel  and 
J.  K.  Moore,  but  the  main  burden  of  the  work  as  well  as  the  writing  up 
of  the  report  fell  on  him.  To  his  ingenuity  in  experimentation  and  to 
his  energy  and  enthusiasm  are  due  the  credit  for  the  excellent  results 
obtained. 

The  testing  of  the  paving  brick  made  from  the  various  clays,  aside 
from  the  rattler  tests,  were  made  in  the  Laboratory  of  Applied  Mechanics 
of  the  University  of  Illinois,  under  the  direction  of  Professor  Arthur 
N.  Talbot,  Professor  of  Municipal  and  Sanitary  Engineering,  and  in 
charge  of  Theoretical  and  Applied  Mechanics.  The  absorption  and 
transverse  tests  were  made  by  Mr.  C.  H.  Pierce,  Instructor  in  Theoretical 
and  Applied  Mechanics,  and  H.  L.  Whittemore,  Associate  in  Applied 
Mechanics.  In  addition  to  reporting  on  these  tests,  Professor  Talbot 
has  written  on  the  Qualities  of  High  Grade  Paving  Brick,  and  the  tests 
used  in  determining  them, — a  paper  which  adds  materially  to  the  value 
of  the  report  as  a  whole. 

The  rattler  tests  were  made  under  the  direction  of  Mr.  Purdy  in  the 
laboratory  of  the  Department  of  Civil  Engineering  of  the  University. 
Acknowledgments  are  due  to  Professor  Ira  0.  Baker  of  that  department 
for  the  use  of  these  facilities  and  also  for  preparing  the  vary  interesting 
discussion,  the  "Construction  and  Care  of  Brick  Pavements,"  which 
appears  in  the  report. 

To  the  various  authors  and  assistants  employed  in  the  work,  as  well 
as  to  the  numerous  manufacturers  who  have  so  heartily  cooperated  in 
the  investigation,  our  hearty  thanks  are  due. 

It  is  believed  that  the  results  presented  in  this  report  will  prove  of 
large  importance.  The  more  important  may  be  briefly  summarized  as 
follows : 

(1.)  As  a  result  of  Mr.  Purdy's  tests,  a  relation  has  been  established  be- 
tween the  specific  gravity  of  the  test  pieces  burned  at  different  degrees  of 
heat,  and  the  qualities  of  the  resulting  product,  so  that  a  way  is  now  open  for 
testing  at  comparatively  slight  expense  and  with  considerable  security  as  to 
results,  the  various'  clays  believed  to  be  suitable  for  manufacture  into  pavers. 

(2.)  The  origin  of  clays  and  their  relation  to  the  parent  rocks  and  the 
processes  by  which  the  one  comes  from  the  other  are  discussed  in  detail. 

(3.)  It  is  shown  that  by  suitable  treatment  it  is  possible  to  make  satisfact- 
ory pavers  from  a  larger  number  of  clays  than  was  previously  believed  to  be 
possible. 


XIII 

(4.)  It  is  certain  that  suitable  material  occurs  widely  distributed  through- 
out the  State,  and  probable  that  no  considerable  area  is  wholly  destitute  of 
satisfactory  clays. 

(5.)  A  large  amount  of  analytical  data  on  certain  type  clays  has  been  ac- 
cumulated, and  on  further  study  will  probably  lead  to  still  further  scientific 
and  technical  advances. 

(6.)  An  accurate  series  of  comparative  tests  of  a  large  number  of  paving 
bricks  is  furnished  and  valuable  suggestions  are  made  for  the  improvement 
and  refining  of  the  methods  of  testing. 

(7.)  The  methods  of  constructing  and  caring  for  brick  pavements  are 
presented  in  a  simple  statement  suitable  for  general  use,  and  methods  of 
cheapening  the  cost  of  such  pavements  are  pointed  out. 

It  is  believed  that  this  report  will  prove  stimulating  to  the  paving 
brick  industry,  will  point  the  way  to  improvements  in  methods  of  test- 
ing and  manufacturing,  and  will  lead  to  a  large  use  by  our  cities  and 
town  of  our  very  excellent  home  made  paving  material. 

Bespectfully, 

F.  Foster  Bain,  Director. 


PAVING  BRICK  AND  PAVING  BRICK  CLAYS. 

By  C.  W.  Rolfe,  R.  C.  Purdy,  A.  N.  Talbot  and  I.  0.  Baker. 


GEOLOGY  OF  CLAYS. 

[By  C.  W.  Rolfe.] 

Introduction. 

In  order  to  understand  the  geology  of  clays  it  is  necessary  to  think 
of  the  surface  layers  of  the  earth  as  an  immense  chemical  laboratory  in 
which  exchanges  are  taking  place  on  every  hand,  old  compounds  breaking 
down  and  being  replaced  by  new  ones  continually.  In  this  case  it  must 
be  borne  in  mind  that  nature's  laboratory  differs  from  those  with  which 
we  are  familiar  in  that  in  hers  the  conditions  are  not  constant  but  are 
continually  changing,  while  in  ours  they  are  practically  fixed  and 
uniform. 

Elementary  Chemical  Principles — £  1.  In  considering  whether  a  chem- 
ical union  will  probably  take  place  when  two  substances  are  brought  to- 
gether, it  is  necessary  to  think  not  only  of  the  materials  mixed  but  of  the 
conditions  under  which  they  are  placed.  For  example,  oxygen  and 
hydrogen  may  be  mixed  in  a  tube  in  the  proper  proportions  to  form 
water,  and  if  kept  in  the  dark  will  continue  indefinitely  as  a  mechanical 
mixture  of  gases,  but  if  exposed  to  sunlight  or  to  the  passage  of  an 
electric  spark  union  at  once  takes  place.  Again  air  and  illuminating  gas 
may  be  mixed  in  the  cold  without  union,  but  once  the  temperature  is 
raised  to  the  proper  point  the  mass  bursts  into  flame.  Certain  substances 
will  combine  in  the  cold  which  refuse  to  do  so  when  the  temperature  is 
elevated.  Some  unite  under  heavy  pressure  and  separate  again  when  the 
pressure  is  reduced.  Some  unite  in  the  presence  of  a  third  substance, 
which,  however,  does  not  enter  into  the  compound,  and  separate  again 
as  soon  as  that  substance  is  withdrawn.  In  the  ordinary  operations  of 
the  chemical  laboratory,  little  account  is  taken  of  these  things  because 
there  the  conditions  are  either  uniform  or  are  so  easily  controlled  that 
the  operator  gives  little  thought  to  them — he  learns  the  necessary  control 
by  practice  rather  than  by  precept — but  in  nature's  laboratory  where 
conditions  are  constantly  changing  they  come  to  be  of  supreme  im- 
portance. 

Silica  and  Silicic  Acid. — §  2.  If  a  piece  of  ordinary  granite  be  care- 
fully examined,  glassy  grains  will  be  seen  distributed  through  its  mass. 
These  are  particles  of  quartz  or  silica,  a  compound  of  the  element  silicon 
with  oxygen.     The  chemist  designates  this  material  by  the  symbol  SiO, 


Z  PAVING    BRICK    AND    PAVING    BRICK   CLAYS.  [bull.  no.  9 

using  the  first  two  letters  of  the  word  silicon  with  the  first  of  oxygen 
and  adding  a  small  figure  2  to  indicate  that  the  compound  contains  two 
atoms  of  oxygen  for  each  one  of  silicon. 

Under  ordinary  conditions  quartz  is  considered  one  of  the  most  inert 
substances  with  which  we  are  acquainted.  Water  and  the  acids,  other 
than  hydrofluoric,  seem  to  have  little  or  no  attraction  for  it,  and  very 
little  affinity  seems  to  exist  between  it  and  any  of  the  other  elements.  1 I". 
however,  finely-powdered  quartz  be  mixed  with  pulverized  compounds 
of  the  metals  such  as  potash,  soda,  alumina,  oxide  of  iron,  etc.,  the  mass 
saturated  with  water  and  the  whole  raised  to  high  temperature  under 
strong  pressure,  the  quartz  or  silica  will  at  once  unite  with  water  to 
form  an  acid  called  silicic  acid  and  this  will  immediately  unite  with  the 
compounds  of  the  metals  (bases)  mentioned  to  form  silicates. 

So  strong  is  the  newly-formed  acid  that  it  is  able  to  take  the  metallic 
elements  or  bases  out  of  their  combinations  with  other  acids  and  convert 
them  into  silicates.  Under  conditions  of  high  temperature  and  pressure 
we  are  accustomed  to  regard  silicic  acid  as  the  strongest  of  all  our  acids 
and  able  to  displace  any  of  them.  If  a  mass  consisting  of  carbonate 
of  soda,  nitrate  of  potash,  sulphate  of  alumina,  sulphide  of  iron,  oxide  of 
magnesia,  or  other  salts  of  the  common  bases,  be  mixed  with  finely- 
powdered  silica,  suspended  in  water,  and  raised  to  a  high  temperature  in 
a  sealed  vessel,  the  silica  will  unite  with  water,  forming  silicic  acid,  and 
this  will  crowd  out  the  other  acids  and  unite  with  their  bases,  forming 
simple  or  compound  silicates  of  potash,  soda,  alumina,  magnesia  and 
iron,  the  acids  which  were  originally  united  with  these  bases  being  set 
free  and  dissolved  in  the  water.  This,  it  is  believed,  would  be  the  case 
with  the  salts  of  any  acid  which  might  be  placed  in  the  mixture ;  silicic 
acid  being  stronger  than  the  other  acids  under  these  conditions  will 
crowd  them  out  and  unite  with  their  bases. 

If  we  again  examine  our  piece  of  granite  we  shall  see  that  besides 
the  grains  of  glassy  quartz  there  are  several  kinds  of  minerals  which 
enter  into  its  composition.  Further  examination  will  show  us  that  these 
are  all  simple  or  compound  silicates  of  the  above-mentioned  substances 
and  so  we  believe  that  they  were  all  formed  when  the  mass  was  highly 
heated  and  subjected  to  great  pressure.  All  granitoid,  i.  e.  granite-like, 
rocks  are  believed  to  have  been  formed  under  these  conditions. 

§  3.  In  the  preceding  paragraphs  the  term  silicic  acid  has  been  used 
as  though  it  referred  to  a  single  acid,  and  the  word  silicates  as  though 
the  salts  referred  to  were  derived  by  the  union  of  various  bases  with 
this  acid.  While  this  use  is  sanctioned  by  custom,  chemists  know  that 
the  term  silicic  acid  refers  not  to  one  but  to  a  series  of  acids,  and  that 
the  salts  of  these  acids  differ  as  widely  in  their  properties  as  do  those 
of  other  similar  series.  It  has  been  stated  above  that  silicic  acid  is 
formed  by  the  union  of  silica  (SiO*)  with  wafer  (H2O).  SiO  + 
ILO  =  ILSiOs,  or  silicic  acid.  This  union  actually  takes  place  as 
indicated  and  salts  of  the  acid  so  formed  are  among  the  silicates  most 
commonly  met  with;  but  we  also  know  that  one  part  of  silica  may  and 
does  unite  with  two  parts  of  water  to  form  another  acid,  SiO  -f-  2ILO  = 
ILSiOi,  with  another  well-known  series  of  salts  whose  properties  differ 
from  those  of  the  first-mentioned  acid.     In  the  same  way  a  third  acid, 


rolfe.1  GEOLOGY   OF   OLAYS.  8 

SiOs  -)-  3H2O  =  HeSiO,  formed  by  the  combination  of  one  molecule  of 
silica  with  three  of  water,  and  its  union  with  bases,  makes  a  series  of 
known  salts  with  properties  quite  different  from  those  of  either  of  the 
others.  Theoretically,  it  would  be  possible  to  carry  the  series  on  in- 
definitely, each  added  molecule  of  water  making  a  new  acid  whose  salts 
would  have  properties  differing  from  those  belonging  to  other  members 
of  the  series.  We  do  not  yet  know  what  the  limits  of  the  series  really 
are,  but  feel  certain  that  they  are  much  wider  than  those  indicated  in 
most  text-books  on  chemistry. 

Formation  of  Silicates. — §  4.  When  these  acids  unite  with  bases  it  is 
the  hydrogen  atoms  which  are  crowded  out  by  the  base,  ILSiOa  -f-  K2O  = 
KsSiOa  -j-  ILO.  That  is,  if  silicic  acid  (HaSiOs)  is  united  with  potash 
(K2O)  the  K2  will  replace  the  H2  and  potassium  silicate  K^SiCb  with 
water  (H2O)  will  be  formed.  Consequently  the  larger  the  number  of 
replacable  hydrogen  atoms  the  acid  carries,  the  larger  number  of  atoms 
of  base  will  it  unite  with  and  the  larger  will  be  the  proportion  of  base 
to  silica. 

Acids.        Bases.       Salts.       "Water. 

H.Si03  +  K.O  =  KoSi03  +  H,0  or  K.O.SiO,  +  H,0 
H4Si04  +  2KX>  =  K4Si04  +  2H,0  or  2K,O.SiO.  +  2HX> 
H,Si05  +  3K.0  =  K,SiO,  +  3HX>  or  3K2O.Si02  +  3HX> 

and  so  on. 

It  will  be  noticed  that  the  proportion  of  base  to  silica  increases  regu- 
larly as  the  series  advances. 

Other  series  of  acids  are  formed  by  the  union  of  two  or  more  mole- 
cules of  silica  to  form  a  compound  molecule  which  then  combines  with 
one  or  more  molecules  of  water  to  form  acids  which,  by  their  union  with 
bases,  form  series  of  salts  containing  a  greater  proportion  of  silica  than 
those  noted  above.     Examples  are : 

5H2O+2SiO„=H10Si,O9,  the  acid  for  kaolin. 

4KLO+3SiO.=HsSiA0,  the  acid  for  sepiolite. 

45H2O+10Si62=H9OSi10O63,  the  acid  for  rumpfite,  etc. 

§  5.  The  last  three  paragraphs  explain  how  it  is  that  in  the  natural 
silicates  the  ratio  of  bases  to  silica  varies  indefinitely  in  both  directions. 
The  silicates  so  formed  are  not  stable.  Changing  conditions  of  heat, 
pressure,  mechanical  force,  etc.,  as  well  as  variations  in  the  dissolved 
material  carried  by  earthwater,  cause  certain  bases  to  be  replaced  by 
others  and  even  effect  changes  in  the  composition  of  silicic  acid  itself.  In 
this  way  orthoclase  feldspar  (KAlSi^Os)  is  known  to  have  been  transform- 
ed into  albite  (XaAlSisOs)  through  the  replacement  of  potash  by  soda,  and 
into  anorthite  (CaAkSi^Os)  through  the  replacement  of  potash  by  lime 
with  a  change  of  acid  from  2ILO  +  3Si03  =  ILSiaO*  to  2ILO  +  SiO*  = 
ILSiO*,  as  well  as  into  a  large  number  of  minerals  less  closely  relat«'<] 
(§14).  A  glance  at  the  table  of  analyses  of  any  silicate  given  by  Dana 
or  Hintze  will  give  evidence  of  such  replacements,  and  will  show  the 
regular  gradation  from  one  mineral  into  another.  For  example,  in  the 
table  of  analvses  of  orthoclase  we  find  the  potash  and  soda  content- vary- 
ing from  15.21%  K-.65%  Xa  to  2.62%  K-10.52%  Xa  with  the  greatest 
variety  of  intermediate  forms  showing  the  gradual  passage  from  ortho- 
clase to  albite.     It  is  for  this  reason   that    we  often   see  the  chemical 


4  PAVING     BRICK   AND    PAVING    BRICK   CLAYS.  [bull.  no.  9 

formula  for  a  mineral  written  in  this  way  (Mg  Fe)  SiO*,  which  means 
that  a  variable  quantity  of  magnesia  and  iron  are  combined  with  the 
silica.  This  mineral  (MgFe)  SiO«,  forms  the  intermediate  member  of 
a  series  of  which  MgSiO  and  FeSiO  are  the  extremes,  and  the  formula 
covers  all  the  forms  which  are  produced  as  the  composition  is  gradually 
changed  from  that  of  a  silicate  of  magnesia  to  that  of  a  silicate  of  iron 
or  "the  reverse.  Changes  like  these  are  continually  taking  place  in  the 
crystalline  rocks,  some  minerals  being  removed  or  transferred  into  others 
while  entirely  new  minerals  are  being  introduced. 

CHEMICAL  AND   MINERAL   COMPOSITION  OF  GRANITOID  ROCKS. 

§  6.  All  granitoid  rocks  are  made  up  of  minerals  like  the  above  and 
nearly  all  of  these  minerals  are  silicates  of  one  or  more,  often  many, 
bases. 

In  Table  I  (§  8)  which  is  compiled  from  tables  of  analyses  given  in 
Kemp's  Handbook  of  Eocks,  I  have  indicated  the  composition  of  the 
various  groups  of  rocks,  giving  in  each  case  the  upper  and  lower  limits 
and  the  average,  and  in  Table  II  (§  9)  I  have  'listed  the  minerals  which 
are  most  commonly  found  in  these  rocks  and  indicated  the  chemical  com- 
position of  each.  A  careful  study  of  these  tables  will  show  from  what 
minerals  each  of  the  chemical  substances  listed  in  Table  I  is  derived. 

The  analyses  given  are  such  as  would  result  from  the  use  of  ordinary 
methods.  More  refined  analytical  methods  would  prove  that  these  rocks 
contain  all  known  chemical  elements  variously  combined.  Such  analyses 
would  prove  to  us  that  the  crystalline  rocks  form  the  storehouse  from 
which  all  inorganic  materials  have  been  withdrawn. 

Table  III  (§  10)  gives  F.  W.  Clarke's  estimate  of  the  proportion  in 
which  the  more,  abundant  elements  occur  in  the  earth's  surface  layers. 

Principle  Minerals  which  occur  in  the  several  Groups  of  Crystalline  Rocks. 

§  7.     Granite  Group. 

Essential — quartz,  orthoclase  or  albite. 

**Accessory — mica,  amphibole,  pyroxene. 
Syenite  Group. 

Essential — orthoclase  or  albite,  mica  or  amphibole  or  pyroxene. 

Accessory — iron  oxides,  plagioclase,  quartz,  apatite. 
Nepheline-Syenite  Group. 

Essential — orthoclase,  nepheline,  amphibole  or  pyroxene  or  mica. 

Accessory — plagioclase,    iron   oxides,   apatite,    sodalite,    leucite,    cancrinite, 
zircon. 
Diorite  Group. 

Essential — oligoclase,  hornblende,  or  augite  or  biotite. 

Accessory — labradorite,  rhombic  pyroxene,  apatite,  quartz. 
Gabbro  Group. 

Essential. — labradorite  or  anorthite,  pyroxene. 

Accessory — olivine,  quartz,  biotite,  iron  oxides,  apatite,  chlorite,  serpentine. 
Peridotite  Group. 

Essential — absence  of  quartz,  feldspar  and  the  feldspathoids  as  prominent 
ingredients. 


**The  accessory  minerals  are  usually,   but  not  necessarily,  present. 


ROLFE.] 


GEOLOGY   OF   CLAYS. 
TABLE   I. 


Chemical  Composition  of  Crystalline  Rocks,      (after  Kemp). 


a=  averages  of  12  to  30  analyses. 


Silica. 

Alumina 

Sesqui- 
oxide 
of  iron. 

Pro- 
toxide 
of  iron. 

Lime. 

Mag- 
nesia. 

Potash. 

Soda. 

Si02. 

A1203. 

Fe203. 

FeO. 

CaO. 

MgO. 

K20. 

NaaO. 

Granite  group. 

78.95 
to 

63.63 
a. 70. 00 

18.32 

to 
10.22 
a. 14. 92 

6.1 
to 
.15 
a. 1.96 

5.76 

to 

0 

a. 1.11 

4.89 
to 
.29 
a. 1.99 

2.39 
to 
.12 

a.    .57 

8.38 
to 
.89 
4.56 

5.14 

to 
.30 
a. 3. 10 

Syenite  group. 

66.03 
to 
46.11 
a. 58. 73 

20.76 
to 

10.05 
a. 18. 09 

6.77 
to 
1.31 
a. 3. 21 

8.20 
to 
0 
a. 2. 91 

7.82 
to 
.96 
a. 3. 05 

•5.73 
to 
.39 
a. 1.38 

7.70 
to 
3.84 
a . 5 . 53 

8.55 
to 
1.24 
a. 4. 75 

Nepheline  Syenite 
group. 

61.08 
to 

41.37 
a. 53. 47 

24.14 
to 

16.25 
a. 20. 99 

7.76 
to 
.42 
a. 3. 42 

5.97 
to 
0 
a. 1.07 

4.62 
to 

32 
a. 2. 56 

1.97 
to 
.13 
a.   .53 

7.17 
to 
4.63 
a. 5. 80 

11.17 
to 
6.29 
a. 8. 47 

Quartz  Diorite  group 

70.36 

to 

62.43 

a. 66. 55 

17.88 
to 
14.57 
a. 16. 22 

3.05 
to 
.88 
a. 1.86 

3.97 
to 
.34 
a. 1.90 

4.79 
to 
1.73 
a. 3. 23 

4.57 
to 
.64 
a. 2. 22 

4.12 
to 
1.60 
a. 2. 52 

4.91 
to 

3.10 
a. 3. 94 

Diorite  group. 

67.83 
to 
48.19 
a. 57. 20 

18.88 
to 
14.94 
a. 17. 23 

4.92 
to 

0 
a. 1.97 

7.32 
to 

1.09 
a. 4. 55 

8.98 
to 
3.54 
a. 5. 98 

7.36 
to 
1.32 
a. 2. 32 

5.56 
to 
1.11 
a. 2. 32 

6.77 
to 
3.67 
a. 4. 09 

Gabbro  group. 

59.55 
to 
46.28 
a. 52. 55 

28.01 
to 
12.96 
a. 22. 05 

6.60 
to 
.41 
a. 2. 34 

10.20 

to 

0 

a. 4. 66 

13.16 
to 
6.02 
a. 9. 95 

9.78 
to 
2.95 
a. 4. 24 

3.01 
to 
.09 
a. 1.06 

5.83 
to 
.95 
a. 3. 34 

Peridotite  group. 

55.14 
to 
29.81 
a. 43. 11 

11.76 
to 
.25 
a. 5. 40 

15.01 
to 
1.41 

a. 4. 65 

9.94 
to 
3.90 
a. 5. 46 

15.47 
to 

4.06 
a. 9. 40 

32.41 

to 
15.34 
a. 24. 42 

2.48 
to 
0 
a.   .66 

1.48 
to 
0 
a.  .40 

Si=Silicon. 
0=Oxygen. 

Al= 
Fe- 

Aluminum. 
Iron. 

Ca=Calcium. 
Mg=Magnesium. 

Na= 

Potassium. 
=Sodium. 

TABLE  II. 

Table  of  Minerals  common  in  Crystalline  Rocks,  with  the  Chemical  Compo- 
sition of  Each. 

9.     Feldspar  Group. 

Orthoclase— KAlSi3Os. 

Silica  64.7%;  alumina  18.4%;   potash  16.9%. 

Albite— NaAlSi308. 

Silica  68.7%;  alumina  19.5%;  soda  11.8%. 

Anorthite— CaAL  (Si04)„. 

Silica  43.%;  alumina  36.7%;   lime  20.1%. 

Other  feldspars  are  regarded  as  admixtures  of  these  in  varying  proportions. 


Mica  Group. 

Muscovite— H0KAI3  ( Si04)  3. 

Silica  45.2%;  alumina  38.5%;  potash  11.8%;  water  4.5%. 
Biotite—  (HK)2(MgFe)2AL(Si04)3. 

Silica  39%;  alumina  16.9%;  iron  9%;  magnesia  21.9%;  potash  8.8%. 
Other  micas  may  for  our  purpose  be  regarded  as  admixtures  of  these  or 
varieties  containing  small  amounts  of  other  substances. 


b  PAVING    BRICK    AND    PAVING    BRICK   CLAYS.  [bull.  no.  9 

Hornblende  Group. 

Tremolite— CaMg  ( Si03)  4. 

Silica— 57.7%;    magnesia  28.9%;   lime  13.4%. 
Hornblende—  (MgFe)  3Ca(  Si03)  4. 

Silica  55.5%;  iron  6.3%;  magnesia  22.6%;  lime  13.5%.  or 
Silica  40.1%;   alumina  17.6%;   iron  12.3%;   magnesia  17.5%;   lime  12.5%. 
Other  varieties  of  the  hornblende  group  may  be  regarded  as  admixtures  of 
these  or  varieties  containing  small  amounts  of  other  substances. 

Augite  Group. 

Diopside— CaMg  ( Si03 )  2. 
Silica  55.6%;   magnesia  18.5%;   lime  25.9%. 
Hedenbergite— CaFe  ( SiOs )  ,. 
Silica  48.4%;   iron  29.4%;   lime  22.2%. 
Augite— CaMg  ( Si08)  2. 

Silica  52.5%;  iron  3.1%;  magnesia  19.8%;  lime  24.6%,  or 
Silica  50.2%;  alumina  3.8%;  iron  8.4%;  magnesia  16.4%;  lime  20.3%. 
Other  varieties  of  this  group  may  be  considered  as  admixtures  of  .these  or 
varieties  containing  small  amounts  of  other  substances. 

Olivine  Group. 

Olivine  or  peridotite — (MgFe)2Si04. 
Silica  41.2%;  magnesia  50.2%;  iron  8.5%. 

Feldspathoids. 

Nepheline— K,Na(;AlsSi034. 

Silica  44%;  alumina  33.2%;  soda  15.1%;  potash  7.7%. 

Minerals  similar  to  nephelite  also  occur  in  which  a  portion  of  the  soda  is 
united  with  carbonic  and  other  acids. 

Sodalite— Na3Al3  ( Si04)  3+NaCl. 

Silica  36.4%;  alumina  33%;  soda  18.8%;  salt  11.7%. 

Minerals  similar  to  sodalite  also  occur  in  which  a  portion  of  the  soda  is 
united  with  sulphur  acids. 

Leucite— KA1  ( Si03)  2. 

Silica  55%;  alumina  23.5%;  potash  21.5%. 
Quartz — 

SiO,=free  silica  100%. 

Magnetite — Fe304=Iron  72.4%;   oxygen  27.6%. 

Other  oxides'  of  iron. 

Pyrite— FeS2.=Iron   46.6%;    sulphur  53.4.% 

Other  sulphides  of  iron  which  often  also  contain  varying  percentages  of 
other  metals. 

Titanite— CaTiSi05=  30.6%;  lime  28.6%;  titanium  oxide  40.8%. 

Ilmenite— FeTi03.=Iron  36.8%;   titanium  oxide  31.6%;   oxygen  31.6%. 

Spinel — MgAL04.=Alumina   71.8%;    magnesia   28.2%. 

Zircon— ZrSid4.=Silica  32.8%;   zirconia  67.2%. 

Apatite — 3Ca3P208+CaF2  or  CaCL.   Phosphorus  pentoxide  42.3%;  lime  55.5%; 
fluorine  3.8%,  or  Phosphorus  pentoxide  41%;   lime  53.8%;   chlorine  6.8%. 

Topaz—  (AlF),Si04.     Silica  32.6%;    alumina  55.4%;    fluorine  20.7%. 
Garnet — 

A  series  of  minerals  formed  by  the  union  of  alumina,  magnesia,  lime,  iron 
and  oxides  of  other  metals  with  silica. 
Tourmaline — 

A  group  of  minerals  containing  potash,  soda,  magnesia,  lime,  alumina,  iron 
and  oxides  of  other  metals  united  with  boron  and  silica. 


ROLFE.J 


GEOLOGY    OF    CLAYS. 


While  this  list  covers  practically  all  the  minerals  commonly  found  in 
crystalline  rocks,  many  others  occur  in  small  quantities.  The  composi- 
tions assigned  to  the  several  minerals  are  ideal.  The  actual  minerals 
vary  in  the  proportions  of  the  several  ingredients.  They  also  often  con- 
tain small  amounts  of  substances  not  named  here  because  they  are  not 
typical. 

TABLE    III. 

Table  Shoiving  Percentages  of  the  More  Common  Elements  in  the  Surface 
Layers  of  the  Earth  and  the  Symbols  by  Which  They  are  Known. 

§  10. 


1. 

Oxygen,  0. 

47.00% 

12. 

Phosphorus,  P. 

.11%. 

2. 

Silicon,    Si. 

28.23% 

13. 

Sulphur,   S. 

.11% 

3. 

Aluminium,  Al. 

7.99% 

14. 

Barium,   Ba. 

.089% 

4. 

Iron,  Fe. 

4.46% 

15. 

Manganese,    Mn. 

.0847c 

5. 

Calcium,  Ca. 

3.43% 

16. 

Chlorine,    CI. 

.07  % 

6. 

Sodium,  Na. 

2.53% 

17. 

Strontium,  Sr. 

.034% 

7. 

Magnesium,  Mg. 

2.46% 

18. 

Chromium,   Cr. 

.034% 

8. 

Potassium,  K. 

2.44% 

19. 

Zirconium,    Zr. 

.026% 

9. 

Titanium,  Ti. 

.43% 

20. 

Nickel,    Ni. 

.023% 

in. 

Hydrogen,  H. 

.17% 

21. 

Fluorine,  F. 

.02% 

11. 

Carbon,  C. 

.14% 

22. 

Vanadium,  V. 

.02% 

23.  Lithium, 

Li. 

.01% 

ORIGINAL  COMPOSITION   OF   THE  EARTH  S    CRUST. 

§  11.  Geologists  believe  that  there  was  a  period  in  the  history  of  the 
earth  when  its  entire  surface  was  composed  of  crystalline  rocks  like  those 
described  and  that  this  was  so  because  the  whole  earth  was  then  highly 
heated  and  the  atmosphere  was  many  times  denser  than  now.  The  con- 
ditions then  were  exactly  those  that  make  silicic  acid  more  powerful  than 
the  other  acids  and  consequently  it  was  able  to  take  possession  of  all  the 
bases  and  so  form  crystalline  (granitoid)  rocks  which  are  aggregations 
of  silicates. 

These  conditions  probably  did  not  reach  to  any  great  depth,  possibly 
some  tens  of  thousands  of  feet,  and  below  that  the  bases  are  probably 
either  uncombined  or  exist  in  combination  with  each  other.  Let  us  then 
think  of  the  earth  at  this  early  time  as  being  covered  with  a  mantle 
-nine  tens  of  thousands  of  feet  thick  made  up  entirely  of  silicates  and 
that  this  mantle  then  contained  all  the  chemical  elements  with  which 
we  are  familiar,  except  possibly  the  gases  of  the  atmosphere,  and  to 
some  extent  these  also,  locked  up  in  the  form  of  silicates.  As  the  earth 
gradually  lost  its  heat,  let  us  think  of  these  silicates  as  passing  from  one 
form  into  another  under  the  compulsion  of  changing  conditions  of  heat, 
pressure,  etc.,  and  so  come  to  look  upon  these  outer  layers  of  the  earth 
not  as  something  that  is  fixed,  stable,  immutable,  the  symbol  of  all 
that  is  untransformable  and  enduring,  but  as  a  busy  workship  in  which 
the  various  chemical  elements  are  always  trying  to  adjust  themselves  to 
everchanging  conditions  and  are  never  quite  able  to  reach  their  goal. 

After  millions  of  years  of  this  activity,  the  conditions  at  the  surface 
of  the  earth  came  to  be  markedly  different  from  those  which  have  been 


o  PAVING    BRICK   AND    PAVING   BRICK   CLAYS.  [bull.  NO. '9 

described.  During  all  this  time  the  earth  had  been  absorbing  the  gases 
of  the  atmosphere  and  its  pressure  had  been  reduced  to  approximately 
what  it  now  is.  The  absorption  of  gases  made  the  atmosphere  more 
transparent  to  dark  heatf  and  so  permitted  the  earth's  surface  to  cool 
more  rapidly,  and  this  in  turn  allowed  the  water,  most  of  which  had 
mp  to  this  time  been  suspended  in  the  atmosphere,  to  be  precipitated  and 
remain  upon  its  surface. 

The  cooling  of  the  earth's  surface  and  the  reduction  of  atmospheric 
pressure  gradually  destroyed  the  conditions  which  gave  to  silicic  acid  the 
power  to  keep  possession  of  the  bases  in  spite  of  the  presence  of  other 
acids,  consequently  these  acids  feeling  their  newly  acquired  strength  be- 
gan to  assert  themselves,  to  crowd  out  the  silicic  acid,  and  to  unite  with 
its  bases.  Among  these  acids  carbonic  acid  [(H2C03=C02li20  (carbon 
dioxide  +  water]  easily  takes  first  place,  principally  on  account  of  its 
abundance  in  earth-water. 

DECOMPOSITION   OF   GRANITOID  ROCKS. 

General  Agents  and  Processes. — §  12.  All  rocks  and  minerals  are 
porous,  that  is,  the  particles  of  which  they  are  composed  cannot  lie 
against  each  other  in  such  a  way  as  to  occupy  all  the  space,  and  hence 
openings  or  pores  are  left  for  the  passage  of  air  or  water.  This  is  as  true 
of  a  crystal  of  quartz  or  a  diamond  as  it  is  of  the  coarsest  sandstone. 
If  a  crystal  or  fragment  of  any  stone  be  dried  for  several  hours  at  a 
temperature  above  212  deg.  F.,  carefully  weighed  by  a  delicate  balance, 
then  submerged  in  water  and  either  placed  in  a  receiver  from  which  the 
air  has  been  exhausted  or  boiled  for  several  hours,  then  taken  from  the 
water,  the  surface  carefully  dried,  and  the  specimen  weighed  again,  the 
latter  weight  will  be  greater  than  the  former  by  the  weight  of  water 
which  it  has  absorbed.  This  excess  of  weight  used  in  connection  with 
the  specific  gravity  and  the  dry  weight  of  the  specimen,  will  give  the 
pore  space. 
(Wet  weight — dry  weight)  x  specific  gravity 

=  percentage 

dry  weight  of  pore  space. 

Van  Hise  in  his  "Treatise  on  Metamorphism"*  states  that  the  pore 
space  varies  from  a  small  fraction  of  1%  to  50%  or  more,  and  gives  a 
very  pretty  experiment  to  prove  the  presence  of  pores  in  an  apparently 
impervious  material.  In  agate  or  chalcedony  the  pores  are  so  small  that 
the  most  powerful  microscope  fails  to  detect  them,  yet  if  thoroughly 
dried  specimens  be  boiled  in  colored  solutions  the  liquid  will  make  its 
way  into  them  and  change  their  color. 

The  average  pore  space  in  building  stones  is  variously  estimated 
but  as  data  are  insufficient  but  little  reliance  can  be  placed  upon  any 
of  them.  Perhaps  as  fair  an  estimate  as  has  been  proposed  for  all  rocks 
is  13%  which  would  enable  them  to  absorb  about  one  gallon  of  water  for 
each  cubic  foot.  This  may  or  may  not  be  near  the  truth,  but  it  serves 
to  illustrate  the  fact  that  apparently  solid  rocks  when  saturated  carry 

tHeat  radicated  from  a  non-luminous  body. 
*Monograph   48,    U.    S.    Geological    Survey. 


ROLFE.]  GEOLOGY   OF   CLAYS.  9 

large  volumes  of  water.  It  should  also  be  remembered  that  this  water 
is  not  confined  to  the  inter-crystalline  spaces,  but  permeates  the  inter- 
molecular  spaces  as  well,  even  when  they  are  so  small  that  they  cannot 
be  seen  by  the  aid  of  the  microscope. 

§  13.  Under  the  influence  of  gravity,  changes  in  molecular  attraction, 
temperature,  and  mechanical  action,  this  water  is  continually  kept  in 
motion,  but  the  velocity  of  movement  varies  widely.  In  coarse-grained 
rocks  with  large  pore  spaces,  lying  above  the  level  of  ground  water, 
especially  if  cut  by  fissures  or  other  openings  produced  by  mechanical 
or  chemical  action,  the  flow  would  be  relatively  rapid,  but  in  proportion 
as  the  rocks  become  finer-grained,  the  grains  more  angular,  the  structure 
more  compact  and  the  opportunities  for  drainage  less,  the  rate  of  move- 
ment is  reduced  until  it  becomes  so  low  as  to  be  unmeasurable  by  the 
means  at  our  disposal.  Not  only  this,  but  the  flow  varies  widely  within 
the  rock-mass  itself,  being  relatively  rapid  in  the  inter-crystalline  or 
inter-granular  spaces  and  very  slow  in  the  pores  between  the  molecules. 

When  the  rock  lies  near  the  surface,  well  above  the  level  of  ground 
water,  and  is  more  or  less  cut  up  by  joints,  bedding  planes  and  planes 
of  cleavage  or  fracture,  gravity  becomes  the  dominant  cause  of  motion 
and  the  water  flows  downward  toward  the  base  of  the  mountain  or  the 
immediate  valley  of  some  stream,  but  when  it  lies  below  the  level  of 
ground  water,  other  forces  often  become  strong  enough  to  overcome  grav- 
ity entirely  and  the  water  flows  in  the  direction  of  the  least  resistance, 
whether  that  be  upward,  sidewise  or  downward.  Under  these  condi- 
tions water  often  rises  from  great  depths  bringing  increased  temperature 
and  a  load  of  dissolved  material  which  greatly  increases  its  working 
power. 

'The  water  which  circulates  near  the  surface  is  almost  entirely  de- 
rived from  rain.  As  water  falls  through  the  air  it  dissolves  small 
quantities  of  carbonic  and  other  acids  and  so  reaches  the  surface  in  the 
form  of  a  weak  acid  solution.  The  rain-water  which  falls  upon  the  sur- 
face may  be  divided  into  three  portions,  of  which  the  first,  much  the 
smallest,  is  immediately  converted  into  vapor  and  rises;  the  second,  the 
run-off,  does  not  enter  the  ground  but  slides  off  into  nearby  streams, 
while  the  remainder  sinks  into  the  ground  and  fills  the  pores  referred 
to  above.  This  ground-water  represents  a  varying  percentage  of  the 
rainfall,  depending  on  the  physical  condition  of  the  surface  layers.  It 
may  represent  practically  all  the  water  that  falls  or  only  a  very  small 
fraction,  but,  except  in  the  driest  regions,  it  is  always  sufficient  to  keep 
the  surface  layers  moist  and  the  chemical  forces  active.  As  rain-water 
enters  the  rocks  it  carries  its  dissolved  acids  with  it  and  so  brings  them 
into  contact  not  only  with  each  rock  particle,  but  also  with  each  molecule 
of  which  these  particles  are  composed,  and  as  this  contact  usually  occurs 
under  conditions  which  make  carbonic  acid  stronger  than  silicic  acid,  a 
reaction  takes  place  and  the  former  replaces  the  latter.  The  table  of 
rock-forming  minerals  given  above  shows  that  they  are  usually  com- 
plex salts  in  which  several  bases  are  united  with  silicic  acid.  Some  of 
these  bases  are  more  strongly  held  by  the  acid  than  others,  and  it  hap- 
pens that  those  held  with  least  force  by  silicic  acid  „are  most  strongly 
attracted  by  carbonic  acid.  Potash  and  soda  seem  to  be  attacked  first, 
then  lime  and  magnesia,  then  iron,  and  lastly  alumina. 


10  PAVING    BRICK    AND    PAVING    BRICK   CLAYS.  -bull.  no. 

^  14.  The  statement  commonly  made  is  that  carbonic  acid  enters  the 
compound  and  first  breaks  np  the  union  of  the  alkalies,  potash  and 
soda,  with  silicic  acid,  uniting  with  the  bases  and  setting  the  silicic  acid 
free;  that  it  next  attacks  the  lime  and  magnesia  in  the  same  way,  and 
finally  the  iron,  leaving  the  union  between  alumina  and  silica  undis- 
turbed. We  would  then  have,  in  place  of  orthoclase,  carbonates  of 
potash,  soda  and  iron,  and  hydrous  silicate  of  alumina  with  free  silica. 
This  seems  not  to  be  strictly  true.  The  real  reaction  seems  to  be  that 
carbonic  acid  breaks  the  complex  silicate  into  its  elements  and  that  these 
elements  re-unite  to  form  a  large  number  of  compounds  better  suited 
to  the  new  conditions.  This  charge  is  often  so  complete  that  even  the 
union  between  water  and  silica  (which  forms  silicic  acid)  is  broken,  and 
they  unite  in  different  proportions  forming  an  acid  with  different  com- 
position and  properties.  When  drainage  is  defective  and  the  ground- 
water becomes  saturated  with  dissolved  salts,  it  often  happens  that  the 
decomposition  of  a  single  complex  silicate  gives  rise  to  a  large  number 
of  simpler  salts,  some  of  which  are  silicates  and  some  salts  of  other  acids. 

Van  Hise  in  his  "Treatise  on  Metamorphism"  (pp.  372-4.)  gives  a 
list  of  the  more  common  minerals  and  the  varieties  which  result  from 
their  decomposition.  As  examples,  I  have  selected  those  which  follow: 
Orthoclase  alters  to  allophane,  biotite,  cimolite,  damourite,  epidote,  gibbsite, 

halloysite,  kaolin,  ^muscovite,  newtonite,  pyrophyllite,  quartz. 
Biotite  alters  to  chlorite,  diaspore,  epidote,  gibbsite,  hematite,  hydrobiotite, 

hypersthene,   kaolin,    limonite,    magnetite,    quartz,    serpentine,    sillimanite, 

spinel. 
Hornblende  alters  to  augite,  biotite,  calcite,  chlorite,  epidote,  hematite,  mag- 
netite, quartz,  serpentine,  siderite. 
Nephelite  alters  to  albite    (conjectural),  analcite,   diaspore,   gibbsite,  hydro- 

muscovite    (pinite),   hydronephelite,  kaolin,  muscovite,   natrolite,   sodalite, 

thomsonite. 

It  must  not  be  inferred  that  whenever  one  of  these  minerals  decom- 
poses all  the  above-named  alteration  products  result,  but  simply  that 
any  group  of  them  may  be  formed.  It  is  probable  that  many  changes 
not  included  in  the  above  list  take  place. 

Formation  of  Residual  Clays. — §  45.  It  has  been  stated  above  that 
when  acid  solutions  enter  a  rock,  the  acids  unite  most  readily  with  the 
alkalies,  next  with  the  alkaline  earths,  and  then  with  the  iron.  If  the 
water  circulation  is  poor  and  the  solutions  come  to  be  saturated,  most 
of  the  bases  will  be  redeposited,  either  as  silicates  or  salts  of  other  acids 
or  both,  but  if  the  circulation  is  free,  most  of  them  will  be  carried  away 
in  solution  to  be  deposited  elsewhere.  The  acids  of  ground-water  seem 
to  have  much  less  attraction  for  aluminum  than  for  the  other  bases, 
and  so  the  greater  portion  of  this  base  is  allowed  to  form  new  com- 
pounds with  the  free  silicic  acids,  such  as  halloysite  (AhCk  2SiO-|-Aq), 
allophane  (AbCk  SiO,+5ILO,  cimolite  (2AI2O3.  9SiO+6HsO),  colly- 
rite  (2AM)».  SiO,+9ILO),  kaolin  (AhCk  2SiO»+2H20),  schrotterite 
(8AhO.  3SiO2+30H2O),  montmorillonite  (AhCk  4SiO*+H*0+Aq), 
the  zeolites,  etc.  Some  of  the  alumina,  however,  is  nearly  always  re- 
deposited  without  combination  with  silica  in  the  form  of  gibbsite  (AbO. 
3ILO),  diaspore  (AhO.    ILO)  and  other  oxides  or  hydroxides. 


rolfe.J  <.i;<   L    G1     OF    (LAYS.  11 

If  granite  or  a  granitoid  rock  should  completely  decompose  through 

the  action  of  acids  under  conditions  which  afford  perfect  drainage  most 
of  the  potash,  soda,  lime,  magnesia,  iron,  etc.,  would  be  converted  into 
soluble  salts  and  carried  away,  while  the  aluminum  and  magnesium  salts 
would  mostly  be  left  in  the  form  of  hydrous  silicates  and  oxides.  Such 
a  mass  would  be  composed  of  the  minerals  enumerated  in  the  preceding 
paragraph,  would  be  earthy  in  texture,  and  would  have  the  properties 
which  we  assign  to  clay;  in  fact  it  would  be  what  we  call  a  pure  clay. 
No  fixed  composition  could  be  assigned  to  such  masses  because  they 
would  contain  varying  proportions  of  these  minerals  and  others  like 
them.  Deposits  rich  in  allophane,  collyrite.  gihbsite,  etc.,  would  be  high 
in  alumina  while  those  rich  in  cimolite,  montmorillonite,  etc.,  would  be 
high  in  silica.  As  kaolin  has  nearly  the  average  composition  of  this 
group  of  minerals  it  is  customary  to  use  its  name  for  the  whole  mass, 
and  this  custom  is  all  right  if  we  remember  that  deposits  so  named  are 
not  composed  of  a  single  mineral  substance  having  fixed  properties,  but 
of  a  group  of  minerals  whose  properties  vary  among  themselves  quite 
widely. 

A  glance  at  the  table  of  analyses  of  kaolin  (§  IT  )  will  make  this  point 
clear.  Xos.  4  and  10  in  the  table  have  nearly  the  theoretical  composition 
of  kaolin,  while  11  and  12  of  this  table,  T  and  8  of  the  table  of  ball 
clays,  and  S  and  9  of  that  of  flint  clays,  show  too  high  a  percentage  of 
alumina  in  comparison  to  the  silica,  indicating  the  presence  of  gibbsite 
or  some  other  mineral  high  in  alumina,  and  Xos.  1,  2  and  6  are  much 
too  high  in  silica.  These  last  may  be  explained  by  assuming  the  pres- 
ence of  free  silica,  or  of  minerals  higher  in  silica  than  kaolin.  Probably 
the  true  explanation  would  include  both  these  causes. 

Origin  of  Impurities  Occurring  in  Clays. — £  16.  These  tables  (^  IT, 
18,  19.)  show  also  that  small  percentages  of  alkali,  iron  and  the  alkaline 
earths  are  present  in  nearly  all  clays,  even  those  of  thehighest  grades. 
This  is  brought  about  in  three  ways.  It  may  be  due  to  a  lack  of  drain- 
age which  permits  a  recomposition  of  recently-liberated  bases  in  the  way 
described  above.  A  second  explanation  involves  the  fact  that  slight 
differences  in  the  molecular  structure  of  crystals,  even  those  of  the  same 
mineral,  enables  the  acids  to  break  up  some  of  them  much  more  readily 
than  others;  consequently  in  any  mass  resulting  from  the  decomposition 
of  crystalline  material,  a  considerable  percentage  of  unaltered  or  but 
slightly  changed  fragments  of  crystals  is  mixed  with  the  products  of  de- 
composition, and  these  fragments  usually  represent  most  of  the  minerals 
originally  present.  (Users  of  high-grade  clays  usually  remove  the 
coarsest  of  these  fragments,  and  like  minerals  produced  in  other  ways, 
by  washing.)  Or,  third,  they  may  have  been  introduced  by  circulating 
earth-water  bringing  these  ingredients  from  other  sources  and  leaving 
them  in  this  deposit.  All  these  are  real  and  active  causes  for  the  con- 
tamination of  clays. 

From  the  foregoing  we  learn  that  rain-water  falling  on  granitoid 
rocks  sinks  into  them  and  permeates  their  whole  structure;  that  through 
tlv-  action  of  the  acids  which  it  carries,  and  to  some  extent  of  the  water 
itself,  the  silicates  of  which  the  granitoid  rock  is  made  are  broken  into 
their  elements,  and  that  these  enter   into  new  combinations,  the  bases 


12  PAVING   BRICK   AND    PAVING    BRICK   CLAYS.  [bull.  no.  9 

uniting  in  part  with  acids  carried  in  earth-water,  and  in  part  recom- 
bining  with  silicic  acid,  or  with  silicic  acid  and  water  to  form  new 
silicates;  that  in  those  situations  where  the  movement  of  earth-water  is 
free  the  soluble  compounds  formed  by  these  unions  are  carried  away  to 
be  deposited  elsewhere;  that,  in  proportion  as  the  movement  of  earth- 
water  is  obstructed,  these  soluble  salts  enter  into  new  combinations  and 
are  redeposited  as  silicates,  oxides  and  salts  of  other  acids;  that  the 
more  insoluble  salts  formed,  such  as  the  silicates,  hydrosilicates  and 
oxides  of  aluminum  and  magnesium,  and  to  some  extent  of  iron  and 
other  elements,  are  left  behind  as  earthy  masses  containing  fragments 
of  undecomposed  minerals,  and  the  products  of  recrystallization  men- 
tioned above,  mixed  with  the  earthy  matters;  that  as  shown  by  Table  I 
(§  8)  alumina  is  much  more  abundant  in  most  crystalline  rocks  than  any 
other  base,  and  hence  its  salts  enter  more  largely  into  these  earthy  de- 
posits than  do  those  of  any  other;  that  nearly  pure  deposits  of  such 
aluminous  material  cannot  form  unless  the  rocks  from  which  they 
are  derived  are  made  up  almost  exclusively  of  minerals  carrying  as 
bases  only  alumina  and  such  other  substances  as  form  soluble  compounds 
during  decomposition,  and  these  last  only  when  conditions  are  such  as  to 
permit  free  circulation  of  water  during  the  decomposition;  (earthy  de- 
posits of  other  materials  would  be  formed  under  similar  conditions)  ; 
that  these  combinations  of  conditions  rarely  occur,  and  consequently 
high-grade  aluminous  deposits  are  not  common;  that  most  granitoid 
rocks  contain  considerable  percentages  of  magnesia.,  lime,  iron  and  many 
other  substances  not  shown  in  the  tables,  whose  salts,  formed  during  rock 
decomposition,  are  more  or  less  insoluble  and  so  enter  into  the  earthy 
residual  mass,  and  also  that  conditions  which  interfere  with  free  drain- 
age are  more  common  than  those  which  favor  it,  and  so  the  earthy  masses 
generally  contain  the  products  of  the  recomposition  and  redeposition 
of  soluble  salts ;  that  these  residual  masses  of  earthy  aluminous  material 
are  called  clays,  and  that  clays  produced  by  the  decomposition  of  rocks  in 
situ  are  called  residual  clays. 

It  is  also  evident  that  the  composition  of  residual  clays  will  vary 
with  that  of  the  rocks  from  which  they  are  derived,  and  will  include 
nearly  pure  deposits  of  salts  of  alumina  as  found  in  so-called  kaolin,  ball, 
flint  and  fire  clays,  on  the  one  hand,  and  the  very  impure  brick1  tile, 
and  adobe  clays,  on  the  other.  The  variation  in  composition  of  such 
grades  of  clay  as  are  used  commercially  may  be  seen  by  reference  to 
the  following  table  of  analyses  taken  from  the  official  publications  of  the 
United  States,  and  those  of  the  various  states.  The  analyses  are  selected 
with  the  purpose  of  showing  variations  in  composition.  All  are  of  clays 
that  are  highly  esteemed  for  their  several  uses. 


ROLFE.] 


GEOLOGY   OF   CLAYS. 


18 


§  17.  Analyses  of  Typical  Clays. 


kaolin. 


10. 

11. 

12. 


Silica.   Alumina.    Iron. 


King-to-Chin,  China 

Berlin,  Germany 

Sevres,  France 

Cornwall  (best)  England. 

Meissen,  Germany 

Wilmington,  Del 

Wood  bridge,  N.J 

Lawrence  Co.,  Ind 

Inyo  Co.,  Cal 

Edwards  Co.,  Texas 

Elgin,  Scotland 

Steinbruck,  Styria 


73.55 

72.96 
58.00 
46.30 
57.70 
72.40 
44.10 
39.00 
44.74 
45.82 
39.30 
40.7 


21.00 
24.78 
34.50 
39.70 
36.00 
14.80 
39.36 
36.06 
33,23 
39.77 
38.52 
38.40 


1.40 


Lime. 
2.55 
.10 
4  50 
.40 
.30 
.35 


1.63 

.77 


Mag- 
nesia.   Alkalies. 


.23 


M 


.83 
1.50 


3.00 

.50 
5.20 

.75 
14.90 

.54 
2.24 

.39 


Water. 
2.62 


12.  i 


23.50 
17.56 


19  54 
18.00 


Silica. 

Edgar,  Florida 46.11 

Burt's  Creek.  N.  J 44.40 

South  Ambov,  N.  J 44.89 

Mayfield,  Ky 56340 

Wareham,  England 55.00 

Jefferson  Co..  Mo 48.51 

Union.  Mo 44.14 

Hall,  England 39.60 


BALL  CLAYS. 

Mag- 
Alumina.    Iron.       Lime.       nesia.    Alkalies.    Water. 

39.55              .35     13     1378 

38.34              .86 44  14.60 

37.27              .97              .41              .19           1.44  14.47 

30  00     40     5.27  7.93 

29.71           2.14              .62     3.44  10.84 

35.18              .92           1.01            1.47           2.30  10.72 

39.86              ,46              .77              .46              .71  13.84 

45  00     10           3  30     12.00 


Silica. 

1.  Mineral  Point.  0 52.52 

2.  Salinville.  0 59.92 

3.  Beaver  Co.,  Pa 65.85 

4.  Swallow  Falls,  Ind 61.00 

5.  Tipton,   Kv 46.75 

6.  Gorman,  Ky 68.01 

7.  Learburg,   Mo 43.82 

8.  Dry  Branch,  Mo 42.60 

9.  Drake,  Mo 40.50 


FLINT  CLAYS. 

Mag- 
Alumina,    iron.       Lime.       nesia.    Alkalies.    Water. 

31.84              .67              .50              .19              .59  11.68 

27.56           1.03     67  9.70 

22.87  1.14              .53              .37           2.01  6.93 

26.36              .83              .21              .10     11.60 

38.17     11     56  14.03 

24.09            1.01            3.01     3.03 

38.24              .23     ....1.93     73  14.94 

41.88  .62              .28              .20              .54  14.00 
43.22              .31           1.10     51  14.15 


FIRE   CLAYS. 


Silica. 

Stonebridge,  Eng 65.1 

Glenb'g  Star,  Scot 65.41 

Gairnkirk,  Scot 53.40 

Leeds,  Eng 78.60 

Limoges,  France 52.55 

Sevres,  France 42.00 

Climax,  Pa 42.82 

Morrison,  Colorado 71.80 

Hickman,  Ky 84.92 

St.  Lauis,  Mo 61.22 

Greenup,  Ky 46.75 

Gruenstadt,  Germany 47.33 


Alumina. 
22  22 
30.55 
43.60 
15.90 
26.50 
38.96 
40.20 
15.00  . 
10.56 
25.64 
38.17 
35.05 


Iron. 
1.92 
1.70 
1.80 
3.60 
.55 
.85 


1.10 

1.70 

.29 

2.30 


Mag- 
Lime,  nesia.    Alkalies.   Water. 

.90     9.86 

.69  .64  .55     

.60     

.84  .42  .29     

3.00  1.50     16.55 

1.04  .17     19.23 

35  1.24             12.80 

3.80     8.30 

.57  .11              .65               2.09 

.70  .08              .73             10.00 

.57  .12              .07             14.03 

.16  1.11           3.18             10.51 


STONEWARE  CLAYS. 

Silica.  Alumina.  Iron. 

1.  Coblentz,  Germany 55.28  24.19  1.00 

2.  Meillonaus,  France 59.00  22.00  5.05 

3.  Meillonaus,  France 57.26  16.04  12.00 

4.  Roseville,  Ohio 69.35  19.08  1.26 

5.  Putnam  Co.,  Ind 66.18  21.15  5.30 

6.  Bacon  Hill,  Md 65.70  20.30  1.00 


Mag- 
Lime,      nesia.  Alkalies.    Water. 

2.02     5.76 

3.85     11.00 

2.15           4.52     10.46 

.60              .63  2.16  6.59 

.70              .14  .33  4.11 

3.50           1.44  .62  7.60 


BRICK  CLAYS. 


Silica. 

1.  Indianola, la.  (loess) 63.31 

2.  Spencer,  la.  (loess) 52.42 

3.  Mason  City,  la.  (shale)...  54.64 

4.  Carterville,  Ga.  (Alluv)...  69.18 

5.  Madison,  Wis 75.80 

6.  Sayerville,  N.  J 60.18 

7.  Garfield,  N.  J 73.71 


Alumina. 
16.57 
13.04 
14.62 
15.43 
11.07 
23.23 
11.09 


Iron. 
4.06 
6.24 
5.69 
5.83 
3.53 
3.27 
4.30 


Lime. 
1.11 
7.98 
5.16 

"i'M 
1.00 
2.31 


Mag- 
nesia. 
1.10 
2.24 
2.90 
.71 
.08 
.67 
1.71 


Alkalies. 
3.16 


5 
1 
2 

3. 
3.29 


11 


Water. 
10.65 
6.73 
9.39 
6.85 
3.70 
8.54 
3.93 


14 


PAVING    BRICK    AND    PAVING    BRICK   CLAYS. 


[BULL.    NO.   9 


TERRA  COTTA   CLAYS. 

Silica.  Alumina.  Iron.  Lime. 

1.  Baltimore,  Md 68.30         21.27  1.43  .52 

2.  Alfred  Center,  N.  J 53.90         23.25  10.90  1.01 

3.  Billings,  Mo 63.11         23.11  1.79  .42 

4.  Woodbridge,  N.  J 44.20         38.66  .74     


Mag- 
nesia. 
.90 
.62 
.70 


Alkalies. 

.20 
2.69 
3.71 

.46 


Water. 

7.55 

6.39 

7.05 

13  55 


GLACIAL  CLAYS. 

Silica.  Alumina.    Iron. 

1.  Chippewa  Falls,  Wis 71.77  13.74  3.60 

2.  Glenwood,  Wis 73.14  11.14  5.00 

3.  Marshfield.  Wis 68.74  10.65  3.16 

4.  Menomonie.  Wis 63.36  14.01  6.40 

5.  Merrillan.  Wis 62.59  17.42  5.88 

6.  River  Falls,  Wis 70.02  14.77  5.00 

7.  Tomahawk,  Wis 70.41  13.64  5.20 

8.  Whittlesey,  Wis 70.54  13.60  4.48 


Lime. 

1.23 

.97 

3.81 

2.63 

"Y.02" 

1.54 

.70 


Mag- 
nesia. 
1.17 
.88 
2.73 
2.21 
1.29 
1  03 
1.49 
1.41 


Alkalies. 
3.50 
3.68 
4.00 
4.50 
8.60 
3.33 
4.12 
4.30 


Water. 
5.00 
4.58 
6.55 
6.79 
4.15 
4.50 
3.37 
4.10 


LOESS  CLAYS. 


Silica. 

Kansas  City,  Mo 72.00 

Boonville,  Mo 71.11 

Jefferson  City,  Mo 74.39 

Hannibal,  Mo 73.80 

St.  Louis,  Mo 73.92 


Alumina. 
11  97 
11.02 
12.03 
13.19 
11.65 


Iron. 
3.51 

3.90 
4.06 
3.43 
4.74 


Lime. 
1.80 
2137 
1.50 
.86 
1.43 


Mag- 
nesia. 
1.35 
1.47 
1.53 
.68 
.60 


Alkalies. 
3.25 
3.14 
3.01 
2.94 
3.13 


Water. 
5.42 

6.71 
3.17 
5.26 
3.08 


ADOBE  CLAYS. 


Santa  Fe.N.  M... 
Ft.  Wingate,N.M 
Humboldt,  Nev.. 
Salt  Lake  City, 
Utah 


Silica. 
66.69 
26.67 
44.64 

19.24 


Alumina. 
14.16 
.91 
13.19 

3.26 


Iron. 

4.38 

.64 

5.12 

1.09 


Lime. 

2.49 

36.40 

13.91 

38.94 


Mag- 
nesia. 

1.28 
.51 

2.96 

2.75 


Alkalies. 


2.30 


Carbonic  Organic 


acid. 

.77 
25.84 
8.55 

29.57 


matter. 
2.00 
5.10 
3.43 

2196 


Water. 
4.94 
2.26 

3.84 

1.67 


Akron,  O 

Albany,  N.  Y. 


Silica. 
60.40 
58.54 


SLIP  CLAYS. 


Alum- 
ina. 
10.42 
15.41 


Iron. 
5.36 
3.19 


Lime. 


Mag- 
nesia. 
4.28 
3.40 


Alka- 
lies. 
.87 
4.45 


Water. 
8.05 
8.08 


FULLERS  EARTH. 


Silica. 

Reigate,  Germany 53.00 

England 44.00 

Florida 62.83 

Georgia 67.42 

South  Dakota 58.72 


Alum- 
ina. 
10.00 
11.00 
10  35 
10.08 
16.90 


Iron. 
9.75 

10.00 
2.45 
2.49 
4.00 


Lime. 
.50 
5.00 
2.43 
3.14 
4.06 


Mag- 
nesia. 
1.25 
2.00 
3.12 
4.09 
2.56 


Alka- 
lies. 


5.00 
.94 


2.11 


Water. 
24.00 
21.00 
14.13 
11.89 
10.40 


PAVING   BRICK  CLAYS. 


Silica. 

FortSmith,  Ark 58.43 

Cartersville,  Ga 58.63 

Robbins,  Ky 51.56 

Columbus,  O 58 .38 

Massillon,  0 64.10 

Palestine.  O 57.80 

Clinton,  Ind  43.14 


Alum- 
ina. 
22.50 
20.47 
15.56 
20.89 
21.79 
25.54 
40.87 


Iron. 
8.35 
8.58 
7.68 
5.78 
2.51 
2.51 
3.44 


Lime. 


7.27 
.44 
.10 
.25 

2.01 


Mag- 
nesia. 
1.14 
1.42 
.82 
1.57 
.58 
.61 
.97 


Alka- 
lies. 
3.21 
4.00 
3.57 
5.02 
2.65 
2.69 
.02 


Water. 
6.20 
7.06 
13.44 
7.53 
6.05 
8.35 
9.48 


Percentage  of  Clay  Substances. — §  18.  In  a  preceding  paragraph 
(§  16)  the  statement  was  made  that  clay  contains  a  great  variety  of 
Silicates,  hydrosilicates,  oxides  and  hydroxides  of  alumina,,  and  these 
minerals  differ  widely  in  chemical  composition  and  physical  properties. 
It  was  further  stated  that  the  chemical  composition  of  kaolin  comes 
nearer  a  fair  average  of  all  these  minerals  than  any  other.  Assuming 
ifoi*  our  present  purpose  that  it  is  a  true  average,  we  may  use  its  formula 


ROLFE.]  GEOLOGY    OF    CLAYS.  15 

to  estimate  the  amount  of  true  clay  matter  in  any  clay.  This  formula 
tells  us  that  39.5%  of  pure  clay  is  alumina,  or  in  other  words,  that  if  we 
multiply  the  alumina  as  given  in  any  complete  analysis  by  2.53,  we  will 
have  the  proportion  of  true  clay  substance  which  the  commercial  clay 
contains. 

Let  us  take  for  example  the  fourth  analysis  Tinder  the  table  of  kaolins 
(§  17),  which  shows  39.7%  of  alumina;  39.7X2.53=100.4%,  or  the 
material  is  practically  pure  kaolin.  Again  No.  5,  under  brick  clavs, 
shows  11.07%  alumina;  11.07X2.53=28%,  or  only.  28%  of  the  mass 
is  true  clay.  If  we  consider  the  last  analysis  under  ball  clays,  we  have 
alumina  45%.  45X2.53=113.85%,  or  the  alumina  present  represents 
an  amount  of  kaolin  13.85%  greater  than  the  whole  mass.  This  proves 
that  the  clay  is  in  part  composed  of  some  compound  richer  in  alumina 
than  kaolin,  as  gibbsite,  pholerite,  etc.  Further  study  of  the  tables  in 
this  way  will  be  found  instructive. 

If  the  percentage  of  alumina  in  any  such  analysis  be  multiplied  by 
1.176,  the  result  will  be  the  percentage  of  silica,  which  combined  with 
this  alumina  would  form  kaolin.  If  this  factor  be  used  with  the  tables 
it  will  be  found  that  in  quite  a  number  of  instances  the  silica  shown 
in  the  analysis  is  less  than  that  required  for  kaolin,  which  again  proves 
the  presence  of  some  compound  richer  in  alumina  than  kaolin.  In  the 
great  majority  of  instances,  however,  the  amount  of  silica  found  is  less 
than  that  given  in  the  analysis.  This  may  be  explained  either  by  assum- 
ing the  presence  of  free  silica,  or  that  of  a  compound  poorer  in  alumina 
than  kaolin,  as  cimolite.  Usually  the  first  of  these  explanations  is  the 
true  one,  but  the  second  is  occasionally,  we  do  not  know  how  frequently, 
true  also. 

There  seems  little  doubt  that  the  presence  of  compounds  richer  or 
poorer  in  alumina  than  kaolin  will,  in  large  measure,  account  for  differ- 
ences in  behavior  of  clays  whose  analyses  show  similar  compositions. 
This  cannot  be  demonstrated  until  we  know  more  about  the  properties 
of  these  compounds. 

Agents  which  Aid  in  the  Decomposition  of  Rocks. — §  19.  In  §  12,  13, 
14,  15  we  have  shown  how  hard  granitoid  rocks  may  be  decomposed,  by 
earth-water  and  the  acids  which  it  contains,  to  form  an  earthy  mass 
called  clay.  This  process  is  greatly  aided  by  disintegration  produced  by 
alternation  of  heat  and  cold,  freezing  of  water,  mechanical  action  and  ef- 
fect of  organisms.  When  rocks  are  heated  they  expand ;  when  cooled  they 
contract.  This  movement  loosens  the  grains  and  allows  water  to  enter 
more  easily.  When  water  in  pores  or  cracks  freezes  and  expands,  it 
tends  to  break  up  the  rocks  or  at  least:  to  enlarge  the  openings.  Mechan- 
ical force  in  bending,  compressing,  or  stretching  rocks  produces  strain 
surfaces,  cleavage  planes,  joints  and  fractures,  and  occasionally  pul- 
verizes rocks,  all  of  which  aids  the  circulation  of  water,  and  so  decom- 
position. Mechanical  force,  by  bending,  breaking,  compressing  or 
stretching  the  rocks,  also  raises  their  temperature  in  the  areas  in  which 
it  operates,  and  this  heat  is  imparted  to  the  water  and  makes  it  more 
active.  Heated  rocks  often  liberate  caustic  acids,  as  those  of  sulphur, 
boron,  fluorine,  etc.,  which  unite  with  water  and  are  transmitted   by 


16  PAVING    BRICK   AND    PAVING    BRICK   CLAYS.  [bull.  no.  9 

fractures  to  distant  rocks,  where  they  effect  marked  changes.  Many  de- 
posits of  kaolin  and  poorer  clays  doubtless  owe  their  origin  principally  to 
these  gases. 

Plant  roots  when  small  enter  crevices  in  rocks,  and  as  they  increase 
in  size  act  as  wedges  to  widen  the  cracks.  They  also  have  the  power  to 
some  extent  to  eat  their  way  into  rocks  and,  enlarging,  force  off  spalls. 
When  organic  matter  decays,  gases  are  produced  which  are  taken  up  by 
water  and  aid  in  decomposition. 

Depth  of^  Deposits  of  Residual  Clays. — §  20.  The  depth  to  which  the 
decomposition  of  crystalline  rocks  into  clays  may  be  carried  has  never 
been  determined.  It  depends  on  many  local  conditions.  Numerous  in- 
stances are  on  record  where  the  resulting  clays  showed  a  thickness  of 
from  50  to  200  ft.  This  could  only  occur,  however,  in  regions  where  the 
drainage  was  excellent  and  where  the  surface  was  protected  from  erosion. 

FORMATION    OF    SEDIMENTARY    ROCKS   AND    CLAYS. 

E rosin  and  Transportation, — §  21.  As  stated  above,  rain  which  falls 
upon  the  surface  is  divided  into  three  portions ;  one  part  evaporates ;  one 
sinks  into  the  ground;  and  one  slides  off  the  surface  into  the  nearest 
stream  or  drainage  channel.  Water,  like  any  other  body  sliding  down  an 
inclined  plane,  develops  energy,  and  this  energy  enables  it  to  pick  up  and 
carry  obstructions,  not  too  heavy,  which  it  finds  in  its  path.  The  law 
which  governs  the  carrying  power  of  water  is  that  its  carrying  power 
varies  as  the  sixth  power  of  the.  velocity,  i.  e.,  if  a  current  moving  at  a 
given  rate  is  able  to  carry  particles  weighing  one  ounce,  another  current 
moving  with  double  that  velocity  will  carry  stones  weighing  64  ounces. 
This  law  makes  it  clear  that  water  flowing  over  loose  material  will  pick 
up  portions  which  lie  on  its  bed  and  carry  them  away.  Eain  falling  on 
the  surface  of  crystalline  rocks  would  attack  the  more  easily  decompos- 
able and  convert  them  into  earthy  material,  thus  disintegrating  the 
rock  and  covering  it  with  a  loose  layer  made  up  of  clay,  hydroxide  of  iron 
and  other  non-aluminous  earthy  matters,  and  grains  of  undecomposed 
minerals  such  as  quartz,  the  less  readily  decomposable  silicates,  and  the 
more  resistant  crystals  of  feldspar  and  other  aluminous  minerals.  A 
portion  of  the  next  shower  that  falls  will  run  off  the  surface  and  will 
carry  with  it  more  or  less  of  this  disintegrated  material;  the  amount 
depending  on  the  velocity.  If  the  ground  slopes  sufficiently  and  there  is 
no  obstruction  to  the  run-off,  the  loose  material  will  be  carried  away  as 
fast  as  it  is  formed,  but  if  the  flow  is  in  any  way  obstructed,  the  granular 
matter  will  accumulate  and  the  surface  will  soon  be  covered  with  vegeta- 
tion whose  roots  help  to  bind  the  particles.  Where  fallen  leaves  and 
stems  protect  the  surface  they  interfere  with  the  action  of  running  water 
and  so  prevent  removal.  In  mountain  regions  on  steep  forested  slopes 
the  residual  clays  have  often  accumulated  to  a  depth  of  30  to  100  ft.  In 
such  places  the  grains  at  the  surface  are  continually  moving  down  the 
slope  but  so  long  as  the  forest  covering  remains,  this  action  is  so  slow 
that  new  material  is  manufactured  at  the  bottom  faster  than  that  on 
the  surface  is  removed.  So  soon,  however,  as  the  forest  covering  is 
removed,  rapid  erosion  sets  in  and  the  accumulated  material  is  speedily 
carried  away. 


rolfe.]  GEOLOGY   OF   CLAYS.  17 

When  these  surface-waters  with  their  load  of  debris  arc  gathered  into 
a  stream  each  hard  grain  becomes  a  tool  with  which  the  stream  tears  Tip 
it >  bed.  Each  undecomposed  fragment  as  it  is  carried  down  tin-  slope 
acquires  energy  with  which  it  strikes  effective  blows  upon  those  portions 
of  the  stream-bed  or  banks  which  resist  its  progress,  and  in  this  way  it 
loosens  fresh  fragments  which  are  soon  added  to  the  load  carried  by  the 
stream.  It  should  be  remembered  that  the  fragments  so  added  are  not 
decomposed,  but  may  be  called  silt  or  rock  flour. 

Transported  Clays. — £  22.  Whenever  the  slope  of  the  stream-bed  i- 
lessened  the  water  loses  velocity  and  consequently  carrying  power.  It 
is  thus  compelled  to  deposit  the  larger  particles  in  its  load,  and  these 
accumulate  to  form  beds  of  gravel  or  sand  according  to  the  velocity 
which  the  stream  still  retains,  but  the  finer  portions  are  carried  on  until 
some  further  reduction  of  velocity  compels  the  stream  to  drop  them  also. 
In  this  way  running  water  gathers  the  residual  clays  and  other  products 
of  decomposition  from  the  often  widely  separated  deposits  in  which  they 
were  formed,  mixes  their  ingredients,  carries  them  to  points  more  or 
less  distant,  assorts  them  and  deposits  the  coarser  or  heavier  grains  in 
beds  of  sand  or  gravel  while  with  the  finer  portions  it  builds  up  beds  of 
transported  clay. 

If  in  the  places  where  these  clays  are  deposited,  the  current  remains 
practically  constant  for  long  periods,  thick  beds  of  clay  nearly  or  quite 
uniform  in  composition  and  texture  will  result ;  but  as  every  heavy  rain 
which  falls  on  any  part  of  the  area  drained  by  the  stream  increases  its 
volume  and  consequently  its  velocity,  the  places  where  it  deposits  its 
clay  may  change  frequently,  and  consequently  the  deposits  at  a  given 
point  may  form  alternating  layers  of  coarser  or  finer  material,  fine  clay, 
coarse  clay,  sands  or  gravels,  the  thickness  of  the  individual  layers  being 
governed  by  the  amount  of  sediment  the  stream  was  carrying  and  the 
length  of  time  during  which  the  velocity  remained  constant.  Heavy 
deposits  of  transported  clays,  except  as  noted  below,  usually  represent 
old  lake  beds  or  ponds,  into  which  the  clays  are  brought  by  streams.  The 
clay  brought  by  one  of  these  streams  will  usually  be  uniform  in  com- 
position, with  varying  texture,  but  that  brought  by  different  streams 
may  be  different  if  their  drainage  basins  do  not  lie  on  the  same  kinds  of 
rock.  Consequently  the  deposits  in  such  lake  beds  are  likely  to  be  more 
or  less  in  pockets. 

Comparison  of  Residual  and  Transported  Clays. — £  23.  We  can  now 
understand  the  differences  between  such  residual  and  transported  clays 
a-  have  been  described  above.  These  residual  clays  originate  through 
the  decomposition  of  crystalline  rocks.  They  can  only  be  pure  or  of 
high  grade  when  the  rock-  from  which  they  are  derived  are  made  up  en- 
tirely of  minerals  which  contain  only  silieates  of  alumina  and  of  other 
base-  whose  -alt-  formed  with  the  acids  of  ground-water  are  soluble  and 
then  only  when  the  movement  of  the  water  is  free  enough  to  carry  away 
these  soluble  salts  as  fast  as  they  are  produced.  These  condition-  are 
almost  never  met.  The  purest  deposits  usually  contain  crystals  of  quartz 
and  of  other  minerals  which  are  not  readily  attacked  by  the  acid-  of 
ground-water,  and  these  are  removed  before  such  clays  are  used  by  weath- 
—2  G 


18  PAVING   BRICK   AND    PAVING   BRICK   CLAYS.  [bull.  no.  9 

ering  the  clay  or  by  washing,  usually  both.  Granitoid  rocks  usually  con- 
tain a  considerable  percentage  of  minerals  which  carry  iron,  magnesia, 
lime  and  other  bases,  metallic  and  non-metalic,  in  such  quantity  that  they 
do  not  form  soluble  compounds  when  the  rocks  decompose,  and  are  re- 
tained in  the  earthy  residual  mass.  When  the  movement  of  the  water 
is  in  any  way  obstructed,  even  the  soluble  salts  tend  to  reunite  with  silica 
and  precipitate  in  the  form  of  zeolites  and  similar  minerals,  or  are  de- 
posited direct  as  carbonates  or  salts  of  other  acids.  For  these  reasons 
most  residual  clays  are  too  impure  for  use  in  the  manufacture  of  high- 
grade  ware. 

When  the  residual  material  is  carried  away  by  running  water  it  is 
usually  assorted  before  redeposition.  If  it  were  not  for  changing  velocity 
of  currents  all  the  coarser  decomposed  material  would  be  laid  down  as 
separate  beds  of  sand  and  gravel,  and  all  dissolved  matter  would  be  car- 
ried on  to  the  sea  or  find  place  in  some  special  mineral  deposit,  leaving 
the  clay  by  itself  in  relatively  pure  masses.  This  assortment  of  material 
actually  does  occur  occasionally,  and  very  pure  deposits  of  clay  are  some- 
times formed  in  this  way.  It  always  occurs  in  a  greater  or  less  degree, 
but  we  must  not  infer  from  this  that  transported  clays  are  always  more 
nearly  pure  than  those  formed  in  situ.  They  often  are,  but  during  their 
journeys  they  are  exposed  to  many  sources  of  contamination.  Eivers 
erode  their  beds  and  rains  wash  materials  of  various  kinds,  organic  and 
inorganic,  into  the  current,  so  that  it  often  happens  that  the  transported 
clays  are  much  less  pure  than  the  beds  from  which  they  were  derived. 

Re-erosin,  Transportation  and  Final  Deposition  of  Clays. — §  24.  All 
such  deposits  of  transported  clays  as  have  been  described  are  to  be  re- 
garded as  temporary  only.  They  will  in  turn  be  broken  down  and  car- 
ried further.  Whenever  the  debris  of  granitoid  rocks  is  picked  up  by 
running  water  it  starts  on  a  journey  whose  only  end  is  the  sea.  This 
is  as  true  of  that  which  is  carried  in  solution  as  of  that  in  suspension. 
Both  may  find  temporary  lodgment  many  times  on  the  way ;  the  dissolved 
substances  in  the  form  of  ores  and  other  mineral  deposits,  the  suspended 
substances  in  that  of  earthy  masses,  but  all  of  these  will  later  be  taken 
up  again  and  continue  their  journey.  Every  particle  which  enters  into 
the  composition  of  the  original  rock  will  in  time  find  its  way  to  the  sea. 
Arrived  at  the  sea  the  suspended  materials  are  deposited  on  its  shallow 
margin  in  beds  roughly  parallel  to  the  shore  line.  Here  again  the  debris 
is  more  or  less  perfectly  assorted  into  beds  of  gravel,  sand  or  clay,  and 
outside  the  clays  in  the  clear  water,  sea  animals  absorb  the  dissolved  lime 
and  make  of  it  skeletons  and  shells,  which  upon  the  death  of  the  animals 
are  ground  into  lime-sand  and  eventually  consolidated  into  limestones. 
Certain  animals  too  prefer  to  live  in  muddy  or  sandy  water.  These  also 
have  the  power  to  absorb  lime  from  water  and  with  it  to  harden  their 
tissues.  Upon  their  death  their  hard  parts  are  ground  and  built  into 
the  clays  and  sands. 

Variations  in  velocity  of  the  inflowing  stream,  in  tidal  action,  and  in 
storm  waves,  as  well  as  changes  in  level  on  the  sea  margin,  bring  with 
them  changes  in  position  of  the  belts  in  which  the  assorted  materials  are 
laid  down,  and  so  produce  alternations  of  gravel,  sands,  clays  and  lime- 
stones.    As   the  beds   thicken   these   layers   follow   each   other   without 


rolfe  J  GEOLOGY  OF  CLAYS.  19 

regular  sequence  and  so  build  up  masses  of  sedimentary  material,  which 
sometimes  reach  a  thickness  of  thousands  or  even  tens  of  thousands  of 
feet.  In  the  central  part  of  the  Appalahcian  region  such  sediments  are 
thought  to  have  accumulated  to  the  depth  of  60,000  feet. 

Formation  of  Shales. — §  25.  In  such  masses  enormous  pressures  are 
generated,  and  the  water  with  which  they  are  saturated  is  rich  in  dis- 
solved materials  and  moves  but  slowly ;  consequently  in  part  by  precipi- 
tation of  dissolved  material  which  acts  as  a  cement,  in  part  by  recrystal- 
lization  of  amorphous  (colloidal)  matter,  and  in  part  by  pressure  bring- 
ing contiguous  surfaces  so  near  that  they  are  held  by  molecular  attrac- 
tion, the  loose  sediments  are  consolidated  into  conglomerates,  sandstones, 
shales  and  limestones.  The  alternation  of  coarse  and  fine  particles  due 
to  slight  variations  in  the  currents  during  deposition,  together  with  this 
pressure,  develops  a  shell-like,  shaly  structure  in  this  mass  of  clay, 
roughly  parallel  to  the  bedding,  and  partly  on  account  of  the  recrystal- 
lization  of  the  fine  particles  of  clay,  partly  because  of  the  cementation  of 
its  grains  by  dissolved  lime,  iron  or  silica,  or  partly  because  of  the 
simple  cohesion  of  the  plates  and  grains,  the  plasticity  of  the  clay  is 
lost,  but  it  may  be  regained  by  sufficiently  fine  grinding  which  restores 
the  material  to  its  original  condition. 

In  §  26  we  have  shown  how  changes  at  the  seashore,  while  deposits 
were  being  laid  down,  cause  a  layer  of  clay  to  be  over  or  underlaid 
by  one  of  sandstone  or  limestone.  Changes  smaller  than  these  or  of 
snorter  duration  may  incorporate  grains  of  sand  with  the  deposit  of 
clay  and  so  make  it  more  or  less  siliceous.  On  the  other  hand,  trie 
tests  (hard  covering)  of  silica-secreting  animals  and  plants  may  be  de- 
posited in  considerable  amounts  with  the  clays,  and  silica,  which  is  always 
present  in  sea  water,  may  be  deposited  in  the  inter-granular  spaces  of  the 
solidfying  mass.  In  one  or  more  of  these  ways  the  clays  may  become 
•very  siliceous :  in  fact  there  is  a  regular  gradation  between  pure  clay  on 
the  one  hand  and  pure  sand  on  the  other. 

In  the  same  way  lime-secreting  animals  may  live  upon  the  bottom, 
and  their  hard  parts  be  ground  and  mixed  with  the  mud.  Lime  is  also 
often  chemically  precipitated  between  the  grains  of  the  hardening  mass, 
and  so  we  have  a  regular  gradation  between  pure  limestone  on  the  one 
hand  and  pure  clay  on  the  other.  Iron,  too,  may  be  incorporated  in  the 
same  way,  and  so  when  these  clays  are  compacted  into  shales  we  may 
have  calcareous,  siliceous  or  ferruginous  shales  when  these  adulterants 
are  less  in  amount  than  the  clay,  or  argillaceous  limestones,  argillaceous 
sandstones,  etc.,  when  they  are  in  greater  amount.  Shales  then  may 
be  composed  of  absolutely  pure  clay  or  of  clay  mixed  with  lime,  iron, 
silica,  or  any  other  substances  deposited  by  sea  water  from  suspension 
or  solution,  and  this  mixture  may  occur  in  any  proportions.  This  is  so 
true  that  it  is  a  rare  thing  to  find  either  limestone,  shale,  or  sandstone 
which  does  not  contain  appreciable  amounts  of  the  other  ingredients. 

CHANGES  IX  SEDIMENTARY  ROCKS. 

Emergence  of  Sedimentary  Rocks. — §  26.  Owing  to  changes  which 
are  taking  place  in  the  earth's  interior,  the  altitude  of  most  points  on 


20  PAVING    BRICK    AND    PAVING    BRICK   CLAYS.  [bull.  no.  9 

the  surface  has  changed  repeatedly,  and  similar  changes  are  now  tak- 
ing place.  The  gulf  coast  of  the  United  States,  the  coast  of  Norway, 
southern  Fiance,  northern  China,  North  Africa,  and  Chili  are  rising; 
while  the  Atlantic  coast  of  the  United  States,  northern  France,  the 
Netherlands,  southern  China,  Egypt  and  eastern  Australia  are  sinking. 
That  these  changes  in  level  are  not  confined  to  the  coast  is  shown  by  the 
beach  lines  of  all  large  lakes.  The  old  beach  lines  are  not  parallel  to 
those  now  being  formed.  Careful  studies  made  within  recent  years 
show  that  the  northern  end  of  Lake  Michigan  is  now  rising  at  a  rate 
which,  in  the  opinion  of  G.  K.  Gilbert,  would,  if  continued,  cause  the 
lake  to  find  its  outlet  through  the  sag  and  the  Illinois  river  within  a 
few  centuries. 

Such  movements  have  not  been  confined  to  modern  times,  but  have 
been  going  on  in  all  geologic  ages.  That  vast  areas  of  our  present 
continents  have  been  covered  by  the  sea  is  shown  by  the  presence  of 
limestones,  sandstones  and  shales,  all  stratified  and  all  containing  the 
remains  of  salt-water  animals.  It  can  also  be  proved  that  large  areas 
now  covered  by  the  sea  have  once  been  dry  land. 

If  from  most  points  along  the  shore  line  we  make  a  series  of  soundings 
running  directly  away  from  the  shore,  we  will  find  that  the  sea  deepens 
very  gradually  for  a  considerable  distance  and  then  its  bottom  plunges 
suddenly  down  a  steep  incline.  This  sudden  drop  marks  the  true  border  of 
the  continent,  and  may  be  traced  off  the  shore  of  all  continental  masses.  If 
so  traced  on  a  map  this  line  would  be  found  to  divide  the  earth's  surface 
into  two  nearly  equal  portions,  the  continental  masses  and  the  ocean 
basins.  The  earth's  surface  carries  more  water  than  the  true  ocean 
basins  can  hold,  and  consequently  some  of  the  water  overflows  the  lower 
portions  of  the  continents.  As  the  surface  of  the  continent  changes 
in  altitude  this  water  flows  from  point  to  point,  and  so  portions  which 
were  once  dry  land  are  now  covered,  and  portions  which  were  once  under 
the  waters  of  the  ocean  are  now  dry  land. 

It  is  probable  that  every  point  on  the  earth's  surface  has  at  some 
time  formed  part  of  this  submerged  continental  border,  and  some  have 
been  submerged  many  times.  This  will  help  us  to  understand  the 
presence  of  the  rocks  referred  to  above  at  points  now  far  inland,  and 
successive  elevations  and  depressions  will  help  to  explain  their  alter- 
nations. 

Metamorphism  of  Sedimentary  Hocks. — §  27.  These  same  internal 
changes  produce  marked  wrinkles  or  folds  on  the  continental  areas,  which 
we  call  mountains.  The  process  of  folding  develops  so  much  heat  and 
pressure  that  many  of  the  limestones,  sandstones  and  shales  are  trans- 
formed into  marbles,  quartzites  and  slates.  In  some  places  the  heat  and 
pressure  are  so  great  as  to  melt  and  mix  the  rocks,  causing  the  union  of 
silica  with  the  bases  and  so  changing  them  again  into  granitoid  rocks.  As 
these  changes  always  occur  at  great  depths,  and  as  the  movements  once 
started  are  apt  to  recur  at  the  same  point  for  a  very  long  time,  the  heated 
rocks  do  not  soon  regain  their  normal  temperature  and  water  circulating 
through  them  and  passing  from  them  to  other  rocks  acquires  greater 
transforming  power.  Such  waters  passing  through  cracks  and  fissures 
become  powerful  agencies  in  transforming  the  newly  formed  granitoid 


ROLFE.]  GEOLOGY    OF    CLAYS.  21 

rocks  into  masses  of  clay.  As  those  changes  are  most  likely  to  occur  in 
the  walls  of  fissures,  the  clay  deposits  so  formed  are  found  in  veins  and 
pockets  enclosed  in  crystalline  rocks.  As  these  deposits  result  from  the 
decomposition  of  granitoid  rocks  they  differ  in  no  material  way  from  the 
residual  (days  described  above. 

Slates  are  merely  hardened  and  to  some  extent  reerystallized  shales 
which,  when  ground  sufficiently  fine,  recover  the  properties  of  clays. 

Decomposition  of  Sedimentary  Rocks  and  Formation  of  Deposits  of 
Residual  Clays. — §  28.  When  sedimentary  rocks,  such  as  limestones. 
sandstones  and  shales,  which  were  formed  in  the  bed  of  the  ocean,  are 
elevated  into  dry  land,  they  are  immediately  attacked  by  erosive  forces 
which  seek  to  hreak  them  down  and  transport  their  debris  again  into 
the  sea.  In  the  case  of  sandstones  and  shales,  earth-water  dissolves  the 
cement  which  helps  to  hold  the  grains  together,  and,  aided  by  alterna- 
tions of  heat  and  cold,  frost  and  wTinds,  reduces  them  to  masses  of  loose 
material,  which  are  picked  up  and  carried  away  by  running  water  to  be 
assorted  and  redeposited  as  beds  of  gravel,  sand  and  clay.  In  protected 
locations  where  washing  goes  on  but  slowly,  beds  of  shale  are  often  trans- 
formed into  clay  without  removal.  Earth-water  passing  through  these 
beds  may.  when  conditions  are  favorable,  dissolve  the  soluble  salts  which 
they  contain  and  remove  them,  thus  purifying  the  deposit.  Valuable 
deposits  of  residual  clays  may  in  this  way  be  formed  from  relatively  im- 
pure shales.  It  must  be  understood,  however,  that  under  other  condi- 
tions this  same  earth-w^ater  may  carry  impurities  into  the  shales  and 
so  make  them  or  the  clays  derived  from  them  of  lower  grade  than  before. 

In  the  case  of  limestones,  rain-water  carrying  carbonic  acid  in  solu- 
tion enters  the  rock.  The  acid  attacks  the  carbonate  of  lime,  converting- 
it  into  the  bicarbonate  which  is  far  more  soluble,  and  is  consequently 
dissolved  and  carried  away  by  the  water  when  conditions  favoring  drain- 
age prevail.  If  the  limestone  is  pure  it  will  be  entirely  removed  by  this 
process,  but  if  it  contains  sand  or  clay  these  will  be  left  and  accumulate 
into  beds  whose  thickness  sometimes  aggregates  hundreds  of  feet.  Most 
limestones  contain  more  or  less  of  clay  which  was  deposited  with  the 
lime-sand  when  it  was  accumulating  on  the  ocean  bed,  and  so  the  de- 
composition of  a  limestone  usually  leads  to  the  formation  of  a  bed  of 
clay  of  greater  or  less  thickness,  depending  on  the  clay  content  of  the 
rock  and  protection  from  erosion  during  decomposition.  If  the  clay 
deposited  with  the  limestone  was  pure  and  conditions  during  the  break- 
ing down  of  the  rock  were  unfavorable  to  the  introduction  of  impurities 
from  outside,  or  if  conditions  during  decomposition  were  such  as  to 
cause  the  impurities  to  dissolve  and  leach  away,  these  clays  may  be  of 
exceptionally  high  grade.  Some  of  our  very  best  deposits  have  origin- 
ated in  this  way  and  will  be  described  later.  While  deposits  of  this 
character  are  occasionally  formed,  it  is  usually  the  case  that  clays  which 
result  from  the  decomposition  of  limestones  contain  so  much  lime  as  to 
unfit  them  for  anything  but  the  coarsest  wares. 

Clays  which  have  been  derived  from  the  decomposition  of  sedimentary 
rocks  are  classed  with  residual  clays  but  differ  from  them  in  that  they 
were  at  one  time  transported  clays  which  have  been  built  into  these  rocks 
ami   again    recovered  from  them  through  decomposition  without  having 


22  PAVING   BRICK    AND    PAVING    BRICK   CLAYS.  [bull.  no.  9 

undergone  any  material  change  in  composition  or  structure.  These 
resemble  transported  clays  more  than  they  do  residual.  When  such  clays 
are  carried  from  their  place  of  origin  by  running  water  they  form  de- 
posits which  do  not  differ  in  any  way  from  those  derived  from  crystalline 
rocks.  In  the  case,  however,  where  sedimentary  rocks  are  metamorphosed 
into  crystalline  rocks,  as  explained  in  §  27,  and  then  broken  down,  the 
clays  undergo  great  chemical  and  physical  changes  during  the  process, 
and  when  recovered  are  in  every  day  like  those  derived  from  original 
granitoid  rocks. 

THE  SPECIAL  ACTION   OF   ICE. 

Ice  as  an  Eroding  and  Transporting  Agent. — §  29.  In  the  preceding 
discussion  we  have  for  the  sake  of  simplicity  omitted  the  part  which  ice 
in  the  shape  of  glaciers  has  played  in  the  formation  of  clays.  At  the 
present  time,  especially  in  temperate  regions,  this  agent  cuts  so  small  a 
figure  that  it  might  almost  be  left  out  of  consideration  entirely,  but 
there  have  been  times  when  this  was  not  true,  and  during  one  of  these 
periods  a  large  portion  of  our  own  country  was  covered  with  thick  de- 
posits of  clay  through  its  action. 

During  the  geological  period  immediately  preceding  the  one  in  which 
we  live,  immense  fields  of  ice  accumulated  over  Labrador  and  over  the 
Keewatin  country  which  lies  just  south  and  west  of  Hudson's  Bay.  These 
ice  fields  increased  in  thickness  until  it  is  believed  they  reached  10,000 
feet  or  more.  This  great  thickness  induced  large  pressures  which  caused 
the  lower  layers  to  behave  as  if  they  were  plastic  and  move  out  from 
under  the  mass,  increasing  the  area  of  the  fields  until  they  united  and 
covered  all  that  portion  of  the  United  States  which  lies  roughly  north 
of  the  37th  parallel  and  east  of  the  100th  meridian. 

For  a  very  long  period  preceding  the  action  of  the  glacier  this  area 
had  been  exposed  to  the  action  of  ground-water  and  had  accumulated 
vast  beds  of  clay  and  other  residual  material  produced  by  the  decom- 
position of  the  underlying  rocks.  As  the  ice  sheet  moved  away  from  the 
centers  in  which  it  accumulated  and  passed  over  these  areas  covered 
with  earthy  accumulations,  it  gradually  picked  up  the  loose  material 
over  which  it  was  passing  and  as  the  motion  of  the  ice  particles  was  one 
of  flowage  in  consequence  of  which  they  moved  upward  and  downward 
as  well  as  on  onward,  the  debris  came  to  be  distributed  throughout  the 
entire  mass. 

Chamberlin's  articles  on  the  glaciers  of  Greenland,  published  some 
years  ago  in  the  Journal  of  Geology,  contain  excellent  illustrations  show- 
ing the  distribution  of  rock  waste  through  the  entire  thickness  of  the 
ice  sheet,  and  give  a  clear  conception  of  the  vast  amount  of  such  mate- 
rial which  was  carried  by  these  glaciers. 

In  an  earlier  section  (§  28)  it  is  shown  that  rock  decomposition  pro- 
ceeds unequally,  and  that  in  consequence  fragments  of  the  original  rock, 
less  readily  decomposed  than  the  rest,  are  imbedded  in  the  earthy  mass. 
These  fragments  vary  from  minute  pebbles  to  boulders  the  size  of  a 
C)-room  house,  so  that  the  debris  carried  by  the  glacier  contains  not  only 
•clay  and  other  results  of  decomposition  but  quantities  of  rock,  sand, 


rolfe]  GEOLOGY   OF  CLAYS.  Z6 

gravel,  and  boulders  as  well.  In  addition  to  this  each  rock  fragment 
which  is  dragged  along  by  the  lower  layer  of  the  glacier  becomes  a 
graver's  tool  which  cuts  away  the  bed  over  which  the  ice  moves,  wearing 
away  both  itself  and  the  surface  over  which  it  is  dragged.  Hundreds 
of  these  glacial  tools  with  their  smoothed  and  striated  surfaces  may 
be  found  in  any  bank  of  glacial  gravel,  and  occasionally  large  boulders 
carry  facets  which  show  that  they  have  been  used  for  this  purpose.  Two 
boulders  lying  near  this  university  are  excellent  illustrations.  One  is 
of  granite  and  weighs  10  or  12  tons,  and  the  other  of  limestone  weighing 
probably  not  less  than  20  tons.  Both  carry  several  facets  beautifully 
striated.  When,  as  in  the  digging  of  the  Chicago  Drainage  Canal,  the 
glacial  debris  is  cleared  from  large  areas  of  underlying  rock,  these  sur- 
faces are  found  to  be  smoothed,  striated  and  grooved  by  the  glacial  mill. 

Through  the  agency  of  this  grinding  action  great  quantities  of  rock 
flour  or  ground  but  undecomposed  rock  debris  (silt)  are  added  to  the 
load  carried  by  the  glacier,  and  the  finer  particles  are  distributed  among 
and  deposited  with  the  clay  and  other  products  of  decomposition,  pro- 
foundly affecting  their  properties.  It  should  be  noted  that  each  kind 
of  rock  over  which  the  glacier  passes  adds  its  quota  to  the  grist  of  rock 
flour  which  the  ice  is  carrying.  There  is  no  other  known  agency  which 
brings  together  such  heterogeneous  masses  of  material  as  glaciers. 

As  the  ice  sheet  moved  forward  into  warmer  and  warmer  latitudes 
it  was  continually  wasted  by  the  heat  of  the  sun,  but  in  spite  of  this 
melting  its  front  would  continue  to  advance  so  long  as  the  rate  of  motion 
exceeded  the  rate  of  melting,  and  as  the  amount  of  heat  to  which  it 
was  subjected  varied  from  day  to  day,  month  to  month,  and  year  to 
year,  the  ice  front  would  continually  change  its  position,  now  advancing 
now  retreating,  as  the  balance  between  rate  of  motion  and  of  melting 
varied. 

Ice  as  an  Agent  of  Deposition. — §  30.  Over  most  of  the  area  covered 
by  the  ice  it  was  an  agent  of  destruction  and  transportation,  picking  up 
any  loose  material  with  which  it  came  in  contact,  and  tearing  away  the 
surface  over  which  it  moved,  but  near  its  lower  end  the  whole  character 
of  its  work  was  changed.  Here  rapid  melting  caused  it  to  deposit 
great  quantities  of  unassorted  material,  and  whether  its  front  moved 
backward  or  forward  in  consequence  of  varying  rapidity  in  melting,  it 
was  continually  dropping  its  load  of  debris.  Near  its  front  the  thick- 
ness of  the  sheet  became  so  reduced  and  the  rate  of  melting  so  rapid  that 
it  no  longer  picked  up  the  loose  material  which  it  found  in  its  path, 
but  overrode  it  and  so  as  it  moved  backward  and  forward  it  added 
layer  upon  layer  to  the  mass  accumulating  on  its  bed.  If  the  excursions 
were  short  and  repeated  many  times  over  the  same  area,  the  successive 
layers  would  build  up  one  of  those  ridges,  which  we  call  terminal  mor- 
aines, because  they  mark  positions  in  which  the  glacier  was  nearly 
stationary  for  a  long  period,  but  if  the  excursions  were  long,  these  layers 
would  build  up  those  broad  level  plains  which  we  call  ground  moraines 
(prairies).  It  was  in  this  way  that  nearly  the  entire  surface  of  Illinois, 
but  especially  its  north -eastern  portion,  was  covered  with  a  thick  coat  of 
glacial  debris  aggregating  from  5  to  10  feet  in  ite  thinnest  portions  and 
250  to  300  feet  in  its  thickest.     The  broad  level  prairies  of  our  state 


24  PAVING    BRICK    AND    PAVING    BRICK   CLAYS'.  [hull.  no.  9 

are  in  genera]  its  ground  moraines  which  the  retreat  of  the  ice  and  the 
obstruction  of  drainage  by  the  terminal  moraines  converted  into  broad 
lakes  in  which  vegetation  grew  and,  decomposing,  imparted  its  black 
color  to  the  accumulating  lake  sediments,  while  the  relatively  narrow, 
hummocky  highland  ridges  are  its  terminal  moraines. 

Characteristics  of  Glacial  Clays. — §  31.  Most,  but  not  all,  of  this  thick 
coating  of  glacial  debris  is  made  up  of  unassorted  material.  In  it  the 
clays  are  mixed  in  all  proportions  with  undeeomposed  rock  particles  and 
with  rock  flour  (silt)  both  derived  from  all  kinds  of  rocks.  This  is  our 
boulder  clay,  and  is  probably  more  variable  in  its  composition  and  prop- 
erties and  more  difficult  to  use  than  any  other  variety  with  which  we 
have  to  deal.  Occasionally  we  find  a  deposit  of  this  material  whose  prop- 
erties lit  it  admirably  for  the  manufacture  of  a  certain  kind  of  ware  and 
sufficiently  uniform  in  composition  and  texture  to  furnish  an  abundant 
supply,  but  this  usually  is  not  true.  The  conditions  under  which  they 
are  deposited  usually  make  the  boulder  clays  exceedingly  variable,  occur- 
ring in  pockets  rather  than  in  large  deposits.  Let  us  understand  that  tha 
rinding  of  heavy  deposits  of  boulder  clays  suitable  for  use  in  the  man- 
ufacture of  any  grade  of  ware,  even  the  best,  is  not  to  be  considered  as 
impossible,  but  rather  as  unusual. 

The  melting  of  the  ice  not  only  caused  the  deposition  of  great  quan- 
tities of  debris  but  produced  large  amounts  of  water  as  well,  and  as  this 
water  moved  away  from  the  points  where  it  originated,  it  picked  up  more 
or  less  of  the  boulder  clay,  and  after  carrying  it  for  some  distance  as- 
sorted and  redeposited  it.  It  is  to  this  assorting  action  that  we  owe  the 
pockets  of  sand  and  gravel  which  we  find  in  glacial  deposits,  and  it  is  to 
the  same  force  that  we  owe  many  of  the  hills  and  ridges  of  sand  or  gravel 
which  rise  above  them.  It  is  to  this  action,  too,  that  we  owe  the  deposits, 
often  small,  but  sometimes  very  large,  of  exceedingly  uniform  clay,  free 
from  pebbles  or  from  any  considerable  irregularities  in  structure,  compo- 
sition or  properties.  We  believe  that  these  masses  were  laid  down  in  lakes 
or  ponds  fed  by  streams  which,  before  entering  the  pond,  had  so  far  lost 
their  velocity  that  they  had  dropped  all  the  gravel  or  sand  which  they 
were  carrying  and  so  brought  only  the  tine  clay-like  materials  which 
sell  led    in  the  quiet  waters. 

When  the  ice  front  retreated  it  left  a  generally  level  but  more  or  less 
billowy  surface  behind  it.  This  character  is  given  to  the  surface  partly 
by  the  unequal  distribution  of  debris  in  the  ice  mass,  and  partly  by  the 
fact  that  large  pieces  of  ice  often  break  from  the  retreating  cliff  and  are 
buried  in  debris  before  they  melt.  This  cover  causes  the  melting  to  go 
on  very  slowly  and  as  it  progresses  the  covering  gradually  settles  and 
forms  a  depression  which  subsequently  becomes  a  pond.  Another  factor 
which  tended  to  produce  these  ponds  or  lakes  was  the  formation  of 
small  ridges  at  points  where  the  ice  front  became  practically  stationary 
for  a  short  time  during  its  retreat.  These  ridges  ran  across  the  natural 
depressions  which  ordinarily  furnish  surface  drainage  and  imponded 
the  water.  These  ponds  were  generally  small  and  the  amount  of  ma- 
terial deposited  in  each  was  small  also,  hut  occasionally  large  and  deep 
depressions  were  formed  and  in  these,  extensive  masses  of  peculiarly 
uniform  clavs  were  laid  down,  so  while  heterogeneity  is  the  most  prom- 


rolfe.J  GEOLOGY   OF   CLAYS.  25 

inent  characteristic  of  the  glacial  clays,  considerable  deposits  having 
just  the  opposite  character  are  not  very  unusual. 

As  tin1  water  flowed  away  from  the  neighborhood  of  the  glacier  it 
formed  large  streams  which  carried  great  quantities  of  glacial  material 
in  suspension.  These  it  worked  over,  assorted,  and  laid  down  in  deposits 
which  differed  in  no  way  from  those  described  in  preceding  sections 
which  treat  of  transported  clays.     §  21,  22,  23,  24,  29. 

Origin  of  Loess. — §  32.  Sometimes  the  water  spread  out  in  broad. 
thin  sheets  which,  having  little  velocity,  deposited  a  fine  silty  mate- 
rial over  broad  areas,  carrying  the  finer  clays  still  further  away.  Later 
when  the  water  had  disappeared  and  the  surface  had  become  dry  this 
silty  deposit,  whether  worked  over  by  the  winds  or  not,  became  loess* 
Such  deposits  may  accumulate  until  they  attain  great  thickness.  As 
the  loess  question  is  a  matter  of  controversy  and  the  way  in  which 
it  was  formed  is  still  unsettled,  it  may  be  well,  without  attempting  an 
extended  discussion,  to  say  here  that  loess  is  a  siliceous  silty  clay.  Si  it 
is  a  finely  granular  material,  usually  composed  in  large  part  of  unde- 
composed  rock  particles,  or  in  other  words  of  rock  flour,  but  often  con- 
taining coarser  clay  granules  as  well.  Loess,  then,  is  largely  made  up  of 
rock  flour,  fine  quartz  sand  and  coarse  clay.  Such  a  deposit  could  only 
be  made  by  an  agent  which  could  assort  its  material,  for  we  know  of  no 
way  in  which  so  large  a  mass  of  uniform  in  texture  could  be  produced 
directly,  hence  deposits  of  loess  must  have  been  produced  through  the 
action  of  wind  or  water  or  of  both.  Wind  and  water,  however,  can  only 
transport,  assort  and  deposit  the  loess.  They  cannot  make  the  silty 
grains,  hence  the  richer  the  transported  material  is  in  silt  the  more 
probable  will  be  the  formation  of  loess  deposits.  Silt  may  be  composed 
of  particles  of  those  minerals  which  resist  decomposition  most  effectively 
and  consequently  more  or  less  of  it  may  be  formed  when  rocks  break 
down  under  the  action  of  ground  Avater  and  other  agents  of  disintegra- 
tion, or  it  may  be  produced  by  abrasion  of  wind,  water  or  ice-borne 
fragments  against  exposed  rock  surfaces,  or  its  grains  may  be  formed 
by  the  agglutination  of  particles  of  clay.  The  following  propositions 
may,  I  think,  be  accepted  as  established. 

The  granular  material  which  we  call  loess  can  be  found  in  most 
earthy  deposits. 

Such  material  is  more  abundant  in  the  deposits  of  dry  than  in  those 
of  humid  regions.  Such  materials  are  more  abundant  in  the  deposits 
of  the  later  glaciers  than  in  those  of  the  earlier  glaciers,  rivers,  or  in 
masses  produced  by  decomposition  of  rocks,  hut  are  found  in  these  also. 

If  such  materials,  no  matter  how  they  originated,  are  properly  assorted 
and  the  different  grades  laid  down  in  separate  masses,  loess-like  deposits 
will  be  formed. 

Water  and  wind  working  separately  or  together  are  the  only  agents 
that  can  effect  this  assortment  and  decomposition. 

Water  would  tend  to  form  broad  sheets  of  nearly  uniform  thickness 
while  winds  would  deposit  their  load  in  heaps. 

Conditions  are  more  favorable  to  the  assortment  and  deposition  of 
loess  in  dry  than  in  ordinarily  humid  regions,  because  there  the  surface 
oftener  becomes  thoroughly  dry  and   consequently  the  winds  are  there 


2<5 


PAVING    BRICK    AND    PAVING    BRICK    (LAYS. 


HULL.    NO.   9 


more  effective  and  because  the  rains  come  in  heavy  local  showers  which 
pick  up  large  quantities  of  the  dry  and  loosened  dust  and  carry  it  into 
streams  which  when  they  leave  their  narrow  beds  and  spread  out  upon 
the  plains  assort  and  deposit  it  again. 

The  large  quantities  of  water  and  sluggish  currents  that  attended  the 
melting  of  the  great  glaciers  were  peculiarly  favorable  to  the  formation 
of  deposits  of  loess. 

Such  granular  deposits  would  whenever  they  become  dry  be  peculiarly 
liable  to  be  worked  over,  transported  and  redeposited  by  winds. 

The  loess  problem  so  far  as  it  concerns  the  history  of  individual  de- 
posits will  not  be  solved  until  we  come  to  understand  the  geographic, 
physiographic  and  climatic  conditions  which  prevailed  during  each 
sub-stage  of  the  glacial  and  post-glacial  periods. 


CLASSIFICATION   OF   CLAYS. 

It  has  seemed  best  to  carry  on  the  discussion  of  the  general  problems 
involved  in  the  geology  of  clays  as  we  have  done  in  the  preceding  para- 
graphs and  then  discuss  the  characteristics  of  each  of  the  groups  of  clays 
and  the  conditions  under  which  they  were  formed  separately. 

§  33.  No  really  satisfactory  classification  of  clays  has  yet  been  pro- 
posed, but  the  following  grouping  adapted  from  Orton  and  Wheeler 
seems  better  suited  to  our  purpose  than  any  classification  we  have  seen. 


High  Grade 
Clays. 


Whiteware  Clays. 


Refractory  Clays. 
^  Pottery  Clays. 


r 


Low    Grade 
Clays. 


Kaolin. 
China  Clay. 
Ball  Clay. 

Plastic  Fire  Clay. 
Flint  Clay. 
Refractoro  Shale. 


Stoneware  Clays  and  Shales. 
Paving-brick  Clays  and  Shales 
Sewer  Pipe  Clays  and  Shales. 
Roofing  Tile  Clays  and  Shales. 

Terra  Cotta  Clays  and  Shales. 
Common     Brick     CJays      and 
Shales. 
t  Drain  Tile  Clays  and  Shales. 


Vitrifying  Clays- 
Brick  Clays. 

Gumbo  Clays. 

Loes  and  Adobe  Clays. 

Slip  Clays. 

Fullers  Earth. 


Kaolin. — §  34.  As  has  already  been  said,  kaolin  results  from  the 
decomposition  of  complex  silicates  whose  principal  base  is  aluminum  and 
whose  other  bases  form,  with  carbonic  acid,  compounds  which  are  soluble 
in  earth-water.  As  used  commercially  the  word  does  not  stand  for  a 
definite  mineral  substance,  but  rather  for  series  of  silicates,  hydro-sili- 


ROLFS.]  GEOLOGY    OF    CLAYS.  Z  i 

cates,  oxides  and  hydroxides  of  aluminum,  or  occasionally  oi'  magnesium. 

.Miner alogically  kaolin  or  kaolinite  is  a  well  defined  mineral  with  the 
composition  H2Al2Si20s>=Al2032Si02.21i20  and  as  this  approximates  the 
average  composition  of  the  whole  group  the  name  is  used  commercially 
to  designate  the  widely  varying  mixtures  of  its  members.  This  will  be 
better  understood  by  study  of  the  table  of  analyses  in  §  17. 

The  minerals  most  commonly  entering  into  commercial  kaolin  are  so 
far  as  known— Kaolinite,  AhO3.2SiO2.2H2O;  Pholerite,  AhO3.SiO2.4H2O; 
Hallovsite,  AhO3.2SiO2.3H2O;  Cimolite,  2Al2O3.9SiO2.6H2O;  Montmoril- 
lonite  AlsOs.4Si(MI20 ;  Pyrophyllite,  4Al2O3.loSiO2.4H2O;  Allophane, 
Ah03.Si02;  Collyrite,  2AhO3.SiO2.9H2O ;  Schrotterite,  8AMk3SiO*. 
3OH2O ;  Gibbsite^  AhO^l-LO ;  Diaspore,  AI2O3.H2O ;  Sepiolite,  2MgO. 
3Si02.2H20 ;  the  Zeolites,  quartz  and  undecomposed  fragments  of  the 
minerals  contained  in  the  original  rock.  Admixtures  of  these  minerals 
when  pure  form  a  white  mass,  pulverulent  or  easily  made  so  by  weather- 
ing, and  but  little  plastic  until  finely  ground,  but  its  lack  of  plasticity  is 
probably  due  to  cementation  of  its  grains.  Absolutely  pure  kaolin  can 
only  be  formed  by  the  decomposition  of  rocks  whose  minerals  contain 
no  bases  which  form  compounds  with  carbonic  or  other  earth  acids  that 
are  relatively  insoluble  in  water,  but  commercially  pure  kaolins  may 
contain  any  light  colored  minerals  which  do  not  act  as  fluxes  or  tend 
to  discolor  the  ware. 

Granitoid  rocks  sufficiently  pure  to  form  such  kaolin  are  occasionally 
found,  but  are  rare,  but  wmen  such  rocks  are  fractured  and  open  fissures 
formed,  these  wounds  are  frequently  healed  by  the  deposition  of  a  sort  of 
scar-tissue  called  vein  rock,  made  up  almost  entirely  of  quartz,  potash 
or  soda  feldspar,  and  light-colored  mica.  These  veins  are  often  sufficient- 
ly pure  to  form  kaolin  of  excellent  quality  when  decomposed.  Ex- 
amples of  this  vein  rock  may  often  be  seen  in  the  ridges  projecting  from 
the  boulders  which  are  sometimes  so  abundant  on  our  prairies. 

Occasionally  when  white  argillaceous  limestones  decompose  they  leave 
a  clayey  mass  sufficiently  pure  to  be  classed  as  a  kaolin. 

Our  deposits  of  kaolin  then  are  formed  in  three  different  ways.  First, 
by  the  decomposition  of  highly  feldspathic  granitoid  rocks;  second,  by 
the  decomposition  of  vein  rocks;  third,  by  the  decomposition  of  white 
argillaceous  limestones. 

Principally  on  account  of  their  lack  of  plasticity  kaolins  are  seldom 
used  alone,  but  they  form  the  basis  of  most  white  or  light  wares,  being 
mixed  for  this  purpose  with  plastic  clays,  flint,  spar,  and  often  small 
amounts  of  ground  bones  and  other  ingredients. 

Ball  Clays. — §  35.  Ball  clays  are  simply  plastic  kaolins.  They  are 
said  always  to  have  been  transported,  but  there  seems  no  good  reason  why 
any  deposit  of  kaolin  should  not  become  plastic  if  exposed  to  conditions 
which  favor  the  movement  of  ground-water  through  its  mass  and  espe- 
cially if  this  movement  is  accompanied  by  considerable  changes  in  tem- 
perature. 

A  study  of  the  table  of  analyses  of  ball  clays  (§17)  shows  that  they 
are  often  somewhat  richer  in  alumina  than  the  kaolins.  This  would 
only  be  true  of  those  which  have  been  transported,  because  in  these  only 
would  the  assorting  power  of  water  come  into  play,  causing  the  coarser 


ZO  PAVING   BRICK   AND    PAVING   BRICK   CLAYS.  [bull.  no.  9 

and  heavier  grains  of  silica  to  be  deposited  as  the  current  loses  velocity 
before  the  finer  and  more  buoyant  grains  of  clay.  They  are  comparable 
in  this  respect  to  washed  kaolins.  This  table  also  seems  to  indicate  that 
ball  clays  are  richer  in  minerals  whose  alumina  content  is  too  high  for 
kaolin  than  are  kaolins,  hut  this  is  more  apparent  than  real  because  the 
presence  of  free  silica  in  kaolin  masks  that  of  minerals  high  in  alumina. 
Ball  clays  are  principally  \\^i\\  to  make  kaolin  more  plastic.  When  used 
alone  they  shrink  badly. 

Deposits  of  ball  clays  occut  as  outwash  aprons  at  the  base  of  highlands 
containing  deposits  of  kaolin.  When  running  water  passes  over  places 
where  beds  of  kaolin  come  to  the  surface  the  clay  will  be  picked  up  and 
carried  to  the  base  of  the  slope.  On  the  way  the  lumps  will  disintegrate 
and  the  flakes  and  granules  of  kaolin  be  separated  and  more  or  less 
broken  up,  and  these  processes  will  develop  plasticity  in  the  mass.  On 
the  way  also  the  residual  kaolin  will  be  assorted  and  at  the  base  of  the 
slope  the  quartz  and  fragments  of  undecomposed  minerals  will  be  de- 
posited before  the  clay  particles,  and  these  last  will  build  up  aprons 
of  pure  plastic  clay  derived  from  non-plastic  kaolin  mixed  with  a  vary- 
ing proportion  of  undecomposed  material. 

In  a  preceding  section  (§  25),  we  have  explained  how  clay  may  come 
to  enter  into  the  composition  of  limestone,  and  in  another  (§  28),  how 
this  limestone  when  it  decomposes  leaves  the  clay  behind  as  a  residual 
product.  If,  as  sometimes  happens,  the  clay  which  was  built  into  the 
limestone  was  nearly  or  quite  pure  kaolin  and  the  limestone  itself  wras 
pure  carbonate  of  lime,  the  residual  clay  would  be  a  fine  quality  of  ball 
clay.  If,  as  is  often  the  case,  the  limestone  decomposed  unevenly  and 
cavities  or  caverns  were  formed  in  the  mass  which  increased  in  size 
until  the  roof  was  too  heavy  to  support  its  own  weight  and  consequently 
broke  down  forming  more  or  less  conical  depressions  on  the  surface, 
called  sink-holes,  these  clays  as  they  were  formed  would  be  washed  into 
and  collect  in  the  sink-holes  making  considerable  deposits  of  the  pur- 
est ball  clay. 

When  beds  of  kaolin  or  of  flint  clay  (described  in  §  40)  are  exposed 
to  the  action  of  the  weather  for  a  sufficient  length  of  time  disintegration 
takes  place  and  the  non-plastic  material  becomes  plastic,  but  in  this  case 
any  undecomposed  granules  in  the  original  mass  will  be  retained  in  the 
ball  clay. 

It  rarely  happens  that  when  deposits  of  clay  containing  impurities 
which  can  be  made  soluble  by  weathering  are  leached,  the  foreign  mat- 
ters are  carried  away  and  pure  ball  clays  left  behind. 

As  may  be  inferred,  deposits  of  a  good  grade  of  ball  clay  are  not  very 
common  because  the  very  agents  which  produce  them  tend  to  bring  into 
them  impurities  of  many  kinds  and  so  render  them  less  pure  than  the 
beds  from  which  they  were  derived.  It  is  but  seldom,  although  it 
sometimes  occurs,  that  earth-water  or  surface  water  is  pure  enough  to 
cause  it  to  work  the  other  way  and  produce  a  purer  instead  of  a  less 
pure  deposit. 

Fire  Clays. — §  3C>.  A  fire  clay  is  one- which  will  withstand  a  high 
temperature  without  softening  to  such  an  extent  as  to  become  mis- 
shapen even  when  subjected  to  considerable  pressure;  which  will  endure 


rolfe.]  GEOLOGY   OF   CLAYS.  29 

rapid  changes  of  temperature  without  shattering;  whose  wares  have. 
sufficient  density  to  impede  the  passage  of  gases  or  liquids  which  would 
attack  it.  and  a  chemical  composition  snch  that  it  will  not  readily  unite 
with  the  gases  which  it  is  Likely  to  meet  in  use. 

It  will  be  seen  that  each  of  these  qualities  is  variable  and  that  in 
consequence  no  fixed  definition  of  a  fire  clay  can  be  formulated.  Let  us 
consider  them  in  order.  First  it  must  withstand  high  temperatures 
without  material  softening.  Authors  assign  widely  different  meanings 
to  the  expression  high  temperatures  as  applied  to  fire  clays,  and  no 
agreement  has  been  reached  as  to  what  temperature  a  clay  must  be 
able  to  withstand  in  order  to  merit  a  place  in  this  class.  Each  user  re- 
gards any  clay  which  will  bear  the  highest  degree  of  heat  which  he  uses 
as  a  fire  clay. 

The  ability  of  a  clay  to  withstand  a  high  temperature  depends  upon  its 
chemical  composition  and  upon  its  physical  constitution. 

The  temperature  at  which  a  clay  softens  is  governed  by  the  presence 
or  absence  of  impurities  which  soften  or  melt  at  a  temperature  lower 
than  that  which  would  produce  a  like  effect  in  the  clay  itself.  It  is  a 
curious  fact  that  the  softening  or  melting  of  one  substance  often  brings 
about  a  similar  change  in  contiguous  materials  which  would  remain  un- 
affected except  for  the  presence  of  the  more  easily  melted  material. 
These  less  resistant  ingredients  of  a  clay  are  called  fluxes.  The  more 
common  fluxes  are  in  order  the  alkalies,  potash  and  soda,  the  alkaline 
earths,  lime  and  magnesia,  protoxide  of  iron,  and  to  a  certain  extent 
sesquioxide  of  iron  and  silica. 

^  37.  It  has  been  found  that  pure  alumina  will  withstand  a  tempera- 
ture higher  than  that  required  to  fuse  Seger's  cone  36,  and  pure  silica 
withstands  cone  35,  but  if  a  small  amount  of  finely  pulverized  silica  be 
mixed  with  alumina  it  induces  slight  fusion  at  a  temperature  less  than 
that  required  to  fuse  either  pure  alumina  or  pure  silica.  If  we  increase 
the  proportion  of  silica  this  effect  increases  also,-  but  so  slowly  as  to  be 
hardly  perceptible  until  the  mixture  contains  25  per  cent  of  silica. 
From  this  point  the  effect  increases  rapidly  with  the  increase  of  silica, 
until  the  proportion  of  alumina  10  to  silica  90  is  reached.  This  mix- 
ture melts  at  cone  30.  Further  addition  of  silica  causes  the  mixture 
to  become  more  and  more  refractory.  It  is  thus  seen  that  silica  al- 
though a  very  refractory  substance  in  itself  becomes  a  flux  when  finely 
divided  and  added  to  alumina.  In  the  same  way  lime  and  magnesia, 
which  are  among  the  most  refractory  substances  known  when  pure,  be- 
come exceedingly  active  fluxes  when  mixed  with  silica  or  alumina  or 
both.  Iron  when  in  the  condition  of  the  sesquioxide  or  iron  rust  does 
not  act  vigorously  as  a  flux  but  the  protoxide  is  very  active.  Potash 
and  soda  are  the  most  active  of  the  common  fluxes.  Another  curious 
fact  is  that  a  given  percentage  of  mixed  fluxes  will  produce  a  more 
marked  effect  than  the  same  amount  of  any  one  of  them  and  that  the 
effect  will  be  greater  the  larger  the  number  of  different  fluxes  contained 
in  the  mixture.  It  will  thus  be  seen  that  the  fluxing  effect  of  im- 
purities in  a  clay  depends  not  only  on  the  amount  of  fluxes  present  or 
upon  their  amount  and  kind,  but  upon  the  number  of  different  kinds 
as  well. 


30  PAVING   BRICK   AND    PAVING   BRICK   CLAYS.  [bull.  no.  9 

The  effect  of  fluxes  on  a  clay  depends  also  on  the  fineness  of  grain  of 
the  clay  as  a  whole  and  of  the  fluxes  in  particular.  A  coarse-grained  clay 
will  stand  more  fluxes  than  a  fine  one,  especially  if  the  fluxes  be  coarse. 
It  will  be  seen  then  that  a  fire  clay  is  likely  to  be  refractory  in  propor- 
tion as  the  percentage  of  alumina  is  high  and  that  of  the  fluxes  low.  It 
is  evident  also  that  a  single  flux  will  have  less  proportionate  effect  than 
a  mixture  and  that  fineness  of  grain  is  a  determining  factor  of  consid- 
erable importance.  A  study  of  the  table  of  analyses  of  fire  clays  (§17) 
will  bring  out  these  facts. 

§  38.  The  temperature  of  fusion  also  depends  upon  the  character  of 
the  fire  to  which  it  is  subjected.  Clays  which  withstand  a  high  temper- 
ature when  exposed  to  a  strongly  oxidizing  flame  will  give  way  at  a  much 
lower  degree  of  heat  if  exposed  to  reducing  conditions. 

Second,  a  fire  clay  must  sustain  rapid  changes  of  temperature  without 
shattering.  This  property  depends  on  its  homogeneity  and  openness  of 
structure.  If  some  of  the  ingredients  of  a  clay  expand  more  with  a  given 
increase  in  temperature  than  others  the  tendency  will  be  for  those  which 
expand  most  to  push  the  others  away  and  weaken  the  whole  structure. 
For  this  reason  the  more  homogeneous  clays  are  more  valuable  in  this 
respect.  It  should  also  be  noted  that  the  larger  the  grains  of  the  im- 
purities the  more  harmful  will  they  be  in  this  way. 

Again,  so  far  as  this  property  is  concerned,  it  is  desirable  that  the 
clay  when  burned  should  have  an  open  porous  structure.  Clay  is  a 
poor  conductor  of  heat,  and  if  its  structure  is  dense  it  takes  a  long  time 
for  the  center  of  a  block  to  become  as  hot  as  the  surface.  The  difference 
in  temperature  between  the  outside  and  inside  of  a  block  is  sometimes 
considerable,  and  the  difference  in  expansion  has  a  strong  tendency  to 
shatter  it.  If,  on  the  other  hand,  the  block  is  porous,  the  heat  finds  its 
way  through  much  more  readily  and  the  tendency  to  fracture  is  less. 
No  generally  accepted  test  has  been  proposed  to  demonstrate  the  proper- 
ties of  a  clay  in  this  respect  although  some  prominent  French  engineers 
claim  that  no  clay  should  rank  as  a  fire  clay  whose  products  shatter 
when  heated  to  redness  and  immediately  plunged  in  cold  water — a  very 
severe  test. 

§  39.  Third,  fire  clays  are  often  made  into  crucibles  in  which  glass 
or  metals  are  to  be  fused.  They  are  also  often  so  placed  that  they  are 
exposed  to  the  action  of  ashes  and  various  furnace  gases.  In  order  to 
withstand  these  conditions  they  require  a  certain  degree  of  density  and 
must  have  a  chemical  composition  such  that  they  will  not  be  readily 
attacked  by  the  substances  to  which  they  are  exposed.  First,  for  the 
above  uses  the  clay  should  contain  an  amount  of  flux  just  sufficient  to 
cause,  it  to  contract  and  fill  the  pore  spaces  during  burning  so  that 
the  wares  will  not  be  readily  penetrated  by  the  liquids  or  gases  to  which 
they  are  to  be  exposed.  It  will  be  noticed  that  this  density  of  structure 
is  a  quality  which  is  not  desirable  in  a  clay  which  is  to  be  subjected  to 
violent  changes  of  temperature.  Second,  if  the  liquids  or  gases  to 
which  the  clays  are  exposed  are  strongly  basic  they  will  attack  a  clay 
rich  in  silica  much  more  readily  than  one  rich  in  alumina.  On  the 
other  hand,  if  they  are  strongly  acid  the  aluminous  clays  will  be  more 
easily  attacked  than  the  siliceous  ones. 


rolfe.]  GEOLOGY   OF   CLAYS.  31 

From  the  above  it  may  be  seen  that  the  term  fire  clay  does  not  stand 
for  a  single  kind  of  clay,  but  for  a  group  whose  only  common  property 
is  the  ability  to  withstand  relatively  high  temperatures,  which  means 
that  they  must  be  high-grade  clays  relatively  free  from  all  fluxing  in- 
gredients. Any  clay  that  is  sufficiently  pure  may  be  used  as  a  fire  clay, 
but  the  better  grades  of  kaolin  and  ball  clay  are  generally  too  valuable 
for  such  use.  Again,  as  shales  or  slates  are  only  clays  whose  physical 
structures  have  been  somewhat  changed  by  pressure  or  heat  or  both 
acting  together,  some  of  them  should  be  and  are  sufficiently  pure  to  be 
used  for  the  manufacture  of  refractory  wares. 

As  weathering  and  leaching  tend  to  remove  the  most  active  of  the 
fluxing  materials  in  clay  they  must  improve  its  refractory  properties 
also,  except  in  so  far  as  they  make  its  component  particles  finer.  It  is 
then  a  question  of  balance  between  these  two  effects  whether  its  refrac- 
tory properties  will  be  improved  by  these  processes  or  otherwise.  There 
is  a  method  of  purification  which  is  thought  to  be  responsible  for  the 
formation  of  many  fire  clays.  Many  of  those  most  widely  used  lie  im- 
mediately below  deposits  of  coal,  and  it  is  generally  believed  that  they 
were  laid  down  in  swamps  before  the  coal  was  -formed ;  that  they  were 
soils  which  supported  and  nourished  the  coal  plants;  and  that  these 
plants  abstracted  from  the  soil  considerable  portions  of  the  alkalies  and 
alkaline  earths  as  well  as  iron  and  other  fluxing  materials  and  built 
them  into  the  coal,  thus  materially  increasing  the  refractoriness  of  the 
clay.  Probably  more  is  made  of  this  process  in  accounting  for  the 
refractoriness  of  clays  than  should  be,  but  nevertheless  it  is  true  that 
any  process  which  removes  fluxes  from  clay  makes  it  more  refractory, 
and  growing  plants  have  this  effect  to  a  degree. 

Flint  Clay. — §  40.  There  is  a  class  of  clays  of  almost  stony  hardness 
having  a  conchoidal  fracture  and  a  structure  so  like  flint  that  they  are 
commonly  known  as  flint  clays.  This  flinty  condition  is  believed  to  be 
due  to  a  process  of  cementation,  the  clays  having  at  some  time  stood 
below  the  level  of  ground-water  under  conditions  which  favored  the  pre- 
cipitation of  such  salts  as  the  ground-water  carried  in  solution.  This 
precipitated  material  cemented  the  clay  particles  and  in  connection 
with  the  weight  of  the  overlying  rocks  induced  the  flint-like  structure. 
There  is  then  no  necessary  relation  between  the  flinty  structure  and 
their  chemical  composition  or  any  physical  property  except  plasticity. 
All  flint  clays  are  non-plastic.  Some  are  rendered  more  or  less  plastic 
by  the  ordinary  grinding  and  kneading  to  which  clays  are  subjected,  but 
some  are  not.  Some  authorities  assert  that  no  mechanical  or  physical 
process  to  which  these  clays  can  be  subjected  will  render  some  of  them 
plastic.  It  is  probable  however  that  wet  grinding  and  kneading  if 
sufficiently  prolonged  will  develop  plasticity  in  any  of  them.  It  seems 
to  be  commonly  accepted  that  all  flint  clays  are  refractory,  but  this  is 
not  true,  for  any  clay  will  become  flinty  if  placed  under  proper  condi- 
tions. It  is  true,  however,  that  most  of  the  deposits  of  flint  clay  which 
are  used  commercially  are  high-grade  clays  and  are  consequently  quite 
refractory.  The  preparation  of  the  poorer  grades  is  too  expensive  to  per- 
mit their  use. 


32  PAVING   BRICK   AND    PAVING   BRICK   CLAYS.  [bull.  no.  9 

Some  very  curious  deposits  are  found  among  the  eroded  limestones 
of  southeastern  Missouri.    They  appear  to  have  Formed  in  sink-holes  Like 

the  ball  clays  of  the  same  region,  but  owing  probably  to  defective  drain- 
age the  clay  particles  have  been  cemented  and  the  flinty  structure  de- 
veloped. Where  these  deposits  have  been  exposed  to  the  weather  and  to 
Leaching  they  have  developed  plasticity  and  have  become  ball  clays.  Most 
of  the  high-grade  flint  clays  could  be  used  in  the  manufacture  of  while- 
ware  if  it  were  not  for  the  excessive  shrinkage  and  the  cost  of  prepara- 
tion. As  it  is,  they  are  rarely  used  except  in  the  manufacture  of  fire 
brick  or  other  refractory  wares.  The  table  of  analyses  (§17)  shows  the 
composition  of  some  of  the  better  known  flint  clays.  It  should  not  be 
inferred,  however,  that  all  flint  clays  are  as  pure  as  those  here  given. 

Pottery  Clays. — §  41.  This  term  does  not  stand  for  any  particular 
group  of  clays  or  for  those  possessing  any  particular  properties  except 
that  they  must  be  sufficiently  plastic  to  be  formed  into  the  ordinary  pot- 
ter's wares  and  must  be  capable  of  being  readily  burned  to  a  pleasing 
color.  The  term  then  covers  any  high  or  low-grade  clay  that  has  these 
characteristics. 

Vitrifying  Clays. — §  42.  A  vitrifying  clay  is  one  whose  ingredients 
melt  at  widely  different  temperatures  and  in  which  the  substances  melt- 
ing at  relatively  low  temperatures  are'  sufficient  in  amount  when  fused  to 
fill  all  the  voids  and  form  a  tough,  nearly  or  quite  impervious  mass. 
It  is  desirable  that  there  be  several  of  these  substances  which  fuse  at 
regularly  increasing  temperatures,  for  in  that  case  the  ingredient  which 
fuses  first  at  once  attacks  that  whose  melting  point  is  next  higher  and 
reduces  it  to  a  pasty  condition  before  its  fusion  temperature  is  really 
reached.  As  the  heat  is  increased  this  pasty  mass  passes  into  a  fused 
condition  and  immediately  attacks  that  ingredient  whose  melting  point 
is  next  higher,  converting  it  into  a  paste.  This  process  continues  as  the 
temperature  rises  until  enough  of  the  pasty  material  is  produced  to  fill 
all  the  voids.  If  the  now  solid  mass  is  cooled  slowly  enough  this  almost 
fused  material  will  become  semi-crystalline  and  will  show  on  fracture 
a  dull  stony  rather  than  a  lustrous  or  glassy  surface.  This  semi-crystal-' 
line  condition  of  the  partially  fused  material  is  one  of  the  factors  which 
makes  the  body  tough  when  burned. 

It  will  be  seen  from  the  above  that  a  vitrifying  clay  must  contain 
enough  relatively  refractory  material  to  form  a  skeleton  or  framework 
which  will  support  the  ware  and  keep  it  from  changing  its  form  dur- 
ing the  vitrifying  process.  The  skeleton  may  be  made  up  of  grains  of 
refractory  clay;  of  relatively  coarse  fragments  of  quartz,  which,  however, 
must  not  1)0  too  large  or  the  resulting  burned  body  will  be  too  porous; 
or  even  of  coarsely  ground  particles  of  the  same  clay  whose  more  finely 
pulverized  portions  become  pasty  and  fill  the  vacant  spaces  between  the 
grains,  always  provided  that  the  range  between  the  melting  points  of 
the  more  and  less  refractory  or  of  the  finer  and  coarser  material  shall 
be  300°  or  more.  This  range  must  be  demanded  until  we  have  learned 
to  build  kilns  which  distribute  heat  more  evenly  than  those  now  in  use. 

That  portion  of  a  vitrifying  clay  which  is  expected  to  form  the  paste 
to  lill  the  voids  should  not  contain  too  large  a  percentage  of  carbonates 
or   other  compounds  which  give  off  gases  at  high  heats,   because  these 


rolfe]  GEOLOGY    OF   CLAYS.  33 

gases  in  their  effort  to  escape  tend  to  form  "blebs"  or  vacant  spaces  in 
the  mass  and  thus  undo  the  very  thing  we  are  trying  to  accomplish. 
Again  all  the  particles  of  carbonate  of  lime  tend  to  give  up  their  car- 
bonic acid  at  the  same  temperature.  This  disassociation  leaves  the  cal- 
cium in  what  is  called  the  nascent  state  in  which  condition  it  attacks 
the  other  ingredients  vigorously  and  tends  to  produce  compounds  which 
soften  at  relatively  low  heat,  and  so  the  presence  of  a  large  amount  of 
nascent  calcium  at  any  one  time  has  a  tendency  to  cause  the  Avhole 
mass  to  soften  suddenly  and  flow  so  quickly  that  it  cannot  be  readily 
controlled.  The  silicates  of  lime  and  the  various  compounds  of  potash, 
soda  and  iron,  although  the  last  somewhat  resembles  lime  in  its  action, 
soften  more  slowly  and  so  give  greater  latitude  in  burning,  and  for  this 
reason  are  considered  more  desirable. 

The  virtrifying  clays  then  are  to  be  looked  on  as  in  all  cases  a  mix- 
ture of  refractory  and  non-refractory  ingredients  with  enough  plasticity 
to  enable  them  to  be  molded  into  desirable  forms  and  which  may  be 
burned  to  a  tough  impervious  mass  without  losing  their  shape.  These 
properties  may  be  found  in  high  as  well  as  in  low-grade  clays,  but  of 
course  are  much  more  rare  in  the  former  than  in  the  latter.  The  man- 
ufacturer of  china  finds  it  necessary  to  make  his  mixtures  artificially 
by  incorporating  ground  feldspar,  flint,  Cornwall  stone  and  other  in- 
gredients with  his  kaolin,  and  in  Holland  and  Germany,  and  at  a  few 
places  in  this  country  as  well,  fluxes  and  even  low-grade  clays  are  mixed 
with  fire  clays  for  the  manufacture  of  pavers.  Vitrified  ware  may  be 
manufactured  from  any  clay  if  it  is  properly  prepared,  the  necessary  ad- 
mixtures made  and  carefully  fired,  but  whether  any  given  clay  can  be  so 
used  commercially  is  a  question  for  each  manufacturer  to  decide  for 
himself. 

There  seems  no  good  reason  for  the  commonly  held  opinion  that  shales 
are  better  suited  to  the  manufacture  of  vitrified  ware  than  other  clays 
except  that  the  manufacturers  of  such  wares  in  this  country  have 
adapted  their  methods  to  the  use  of  shales  and  that  consequently  these 
methods  do  not  lend  themselves  kindly  to  the  use  of  clays  of  other  grades. 
Practically  every  grade  of  clay  has  been  successfully  used  for  the  man- 
ufacture of  these  goods  on  a  commercial  scale. 

Terra-Cotta  Clays. — §  43.  To  the  ceramist  the  term  terra-cotta  sig- 
nifies porous  unglazed  as  distinguished  from  faience  or  porous  glazed 
ware,  but  in  common  use  the  term  is  restricted  to  high-grade  artificial  or 
ornamental  wares  having  the  above  characteristics. 

Clays  for  these  purposes  must  be  even-grained  and  smooth-working, 
fairly  plastic  with  good  binding  power,  and  capable  of  being  burned  to  a 
uniform  pleasing  color.  These  qualities  call  for  a  clay  of  uniform  com- 
position and  texture  which  may  be  produced  by  weathering  of  residual 
masses,  but  is  more  usually  formed  by  decomposition  from  bodies  of 
water  which  have  a  slight  but  uniform  current.  As  natural  deposits 
having  all  these  characteristics  are  not  abundant,  the  manufacturer 
usually  reaches  his  ends  by  washing  and  mixing  several  clays  of  uniform 
texture  which  by  their  combination  will  give  the  other  qualities  desired. 

—3  G 


34  PAVING   BRICK   AND    PAVING    BRICK   CLAYS.  [bull.  no.  9 

Some  of  the  most  progressive  manufacturers  of  these  goods  now  use 
vitrifying  clays  and  burn  them  until  the  wares  are  impervious,  thus  re- 
moving them  from  this  group  entirely. 

Brick  Clays. — §  44.  This  group  is  hard  to  describe  because  the  re- 
quirements for  brick  are  passing  through  a  transition.  Formerly  any 
plastic  clay  with  reasonable  binding  power  fired  to  a  heat  somewhat  above 
the  end  of  the  water-smoking  period  would  meet  all  requirements.  Then 
came  the  demand  for  face  brick  with  definite  shape,  smooth  surface, 
and  uniform,  well-defined  colors,  which  made  requirements  the  same 
in  kind  and  nearly  as  exacting  as  those  placed  upon  the  manufacturer 
of  terra-cotta,  Now  the  trade  begins  to  ask  that  these  same  wares  shall 
be  vitrified  and  so  rendered  non-absorbent.  This  last  requirement  has 
probably  come  to  stay,  and  in  a  short  time  only  vitrifying  clays  will  be 
u*(>(\  for  the  manufacture  of  brick.  Then  only  clays  which  have  sufficient 
plasticity  to  enable  them  to  be  molded  into  definite  forms,  sufficient  bind- 
ing power  to  give  the  necessary  strength,  such  openness  of  structure  as 
will  permit  them  to  dry  without  cracking,  such  coloring  ingredients  as 
will  cause  them  to  take  on  a  uniform  and  pleasing  tint  when  properly 
burned,  and  such  chemical  and  physical  characteristics  as  will  give  them 
a  wide  vitrifying  range  will  be  used  for  the  manufacture  of  brick.  Such 
clays  will  be  found  among  the  somewhat  impure  residual  deposits  and 
the  better  grades  of  alluvial  and  diluvial  clays. 

Drain  Tile  Clays. — §  45.  The  requirements  for  a  drain  tile  clay  are 
sufficient  plasticity  to  permit  its  being  readily  molded  into  pipes,  suffi- 
cient binding  power  to  give  it  such  strength  as  will  withstand  handling 
without  breakage,  and  such  openness  of  structure  as  will  enable  it  to 
dry  quickly  without  cracking  and  give  it  after  it  is  burned  such  porosity 
as  will  enable  water  to  pass  through  it  readily. 

These  requirements  call  for  the  lowest  grades  of  clays  and  shales 
usually  carrying  considerable  quantities  of  lime  carbonate  or  sand  or 
both,  and  often  a  considerable  admixture  of  soil  to  give  the  ware  sufficient 
porosity.  Of  course  any  clays  of  higher  grades  which  possess  the  prop- 
erties designated  above  could  be  used  if  it  seemed  desirable  to  do  so. 

Gumbo  Clays. — §  4G.  These  are  composed  of  exceedingly  fine  clay-like 
material  which  packs  so  closely  that  water  passes  through  it  but  slowly. 
It  was  laid  down  in  still  water,  the  streams  which  brought  it  having 
deposited  all  sediment  coarser  than  the  finest  sand  and  clay,  because  of 
loss  of  velocity,  before  reaching  this  point.  It  is  very  plastic  and 
possesses  great  binding  power,  but  dries  slowly  and  cracks  badly.  Such 
clays  when  black  are  called  gumbo,  but  when  lighter  in  color,  hard  pan. 
The  black  color  is  due  to  the  admixture  of  a  considerable  amount  of 
organic  matter. 

These  clays  are  much  used  in  some  parts  of  the  country  to  manu- 
facture road  ballast.  Windrows  of  cordwood  are  covered  with  a  thick 
coating  of  clay  and  fired.  The  wood  burns  slowly  and  imparts  sufficient 
heat  to  the  clay  to  drive  off  the  combined  water.  As  the  clay  shrinks 
badly  it  breaks  up  under  the  influence  of  heat  into  angular  fragments 
which  are  found  to  be  excellent  material  for  ballasting  roads. 


koi.fe.J  GEOLOGY   OF    CLAYS.  35 

Loess  and  Adobe  Clays. — §  \\.  Loess  and  its  methods  of  format  ion 
have  already  been  sufficiently  described.  It  is  Largely  used  in  the  man- 
ufacture of  building  brick  and  to  some  extent  also  for  vitrified  ware. 

Adobe  is  a  very  similar  material  found  in  the  western  states  as  out- 
wash  plains  formed  by  streams  which,  swollen  by  cloudbursts,  pick  up 
great  quantities  of  detritus  produced  by  the  decomposition  of  underly- 
ing rocks,  and  as  they  spread  out  upon  the  plains  and  lose  velocity,  drop 
first  the  coarser  particles,  sands  and  gravels,  which  they  are  bearing, 
then  the  silty  material  mixed  with  coarser  clay  which  is  called  adobe, 
and  carry  the  finer  clay  to  more  distant  points. 

Adobe  is  much  used  by  the  inhabitants  of  Arizona  and  Xew  Mexico 
in  the  manufacture  of  unburned  bricks,  often  reinforced  with  chopped 
straw,  with  which  they  construct  their  houses.  In  that  dry  climate 
with  but  little  rainfall  such  buildings  are  found  to  be  very  satisfactory. 

Fullers  Earth. — §  48.  Fullers  earth  was  formerly  much  used  for 
removing  grease  from  woolen  cloth.  It  is  a  silty  clay  having  little  plas- 
ticity, but  carrying  a  large  amount  of  combined  water.  Clay  has  a 
strong  affinity  for  oils  and  fats,  as  may  be  seen  by  the  following  experi- 
ment: Add  a  teaspoonful  of  oil  to  a  glass  of  water,  then  drop  into  the 
water  a  lump  of  clay  and  stir  vigorously  for  some  time.  If  the  clay  is 
now  allowed  to  settle  it  will  be  noticed  that  the  oil  has  partially  or 
wholly  disappeared,  depending  on  the  amount  and  character  of  the  clay 
used.  Each  particle  of  the  clay  has  been  covered  by  a  film  of  oil  and 
has  carried  it  to  the  bottom  of  the  vessel.  This  experiment  explains 
why  fullers  earth  is  now  so  largely  used  in  purifying  oils.  It  may  also 
be  used  for  taking  grease  spots  from  cloth. 

Minor  Uses  for  Clays. — §  49.  Clay  is  also  largely  used  in  the  manu- 
facture of  portland  cement,. and  to  a  less  extent  as  mineral  paint,  filler 
for  paper,  in  confectionery  and  as  an  adulterant  in  various  foods,  in  the 
manufacture  of  various  soaps,  window-cleaning  and  polishing  powders, 
in  the  manufacture  of  medical  plasters  used  to  subdue  inflammation,  as  a 
retardant  to  the  setting  of  the  cements  now  much  used  in  place  of  lime 
mortar,  and  in  the  manufacture  of  alum,  but  the  quantities  used  in  these 
industries  are  not  sufficient  to  warrant  a  separate  description  in  a 
paper  of  this  kind. 


GEOLOGICAL  DISTRIBUTION  OF  PAVING  BRICK 
MATERIAL  IN  ILLINOIS. 

[By  C.  W.  Rolfe.] 


Introduction. 


What  is  a  Paving  Brick? — Before  discussing  the  distribution  of  pav- 
ing brick  materials  it  seems  best  to  at  least  attempt  to  define  what  a 
paving  brick  is. 

Pages  enough  to  make  a  fair-sized  library  have  been  written  in  the 
effort  to  describe  the  properties  which  a  paving  brick  should  possess  and 
to  formulate  a  series  of  tests  which  would  enable  a  man  always  to  select 
the  best  among  the  samples  submitted  to  him,  but  no  satisfactory  con- 
clusion has  yet  been  reached.  The  chapter  by  Professor  Talbot  which 
appears  in  this  volume  is  an  admirable  presentation  of  our  knowledge  on 
this  subject;  but  all  that  is  really  known  may,  I  think,  be  condensed 
into  the  following  definition :  A  paving  brick  is  a  rectangular  block 
of  burned  clay  which  possesses  in  a  prominent  degree  the  properties  of 
hardness  and  toughness.  It  must  be  hard  in  order  that  it  may  wear  as 
slowly  as  possible  under  the  severe  abrasion  to  which  it  is  subjected.  It 
must  be  tough  so  that  it  will  not  be  broken  or  crushed  by  the  shocks 
which  it  receives. 

While  every  paving  brick  must  possess  both  the  properties  named 
some  lack  in  toughness  is  not  so  serious  a  matter  as  a  lack  in  hardness, 
if  the  pavement  is  properly  laid,  because  in  that  case  all  surfaces  but  one 
are  thoroughly  supported  and  it  would  require  an  unusually  severe 
shock  to  shatter  it.  In  the  streets  of  Champaign  and  Urbana  are 
several  miles  of  pavements  made  from  brick  so  brittle  that  they  required 
the  most  careful  handling  to  place  them  in  the  pavement  unbroken,  yet 
they  have  withstood  wear,  unusually  severe  for  a  country  town,  for  more 
than  a  decade  without  serious  injury.  These  brick  were  made  from 
ordinary  surface  glacial  clay  and  burned  hard.  They  were  so  brittle 
that  most  of  them  would  have  made  a  very  poor  showing  in  a  rattler. 
If,  then,  the  brick  are  very  hard  and  are  properly  supported  on  the 
bottom,  sides,  and  ends,  we  can  overlook  some  deficiency  in  the  way  of 
toughness,  although  of  course  every  effort  possible  should  be  made  to 
secure  as  great  a  degree  of  toughness  as  possible. 

What  is  a  Paving  Brick  Clay? — In  order  to  answer  this  question  in- 
telligently we  must  know  what  properties  a  clay  must  possess  and  what 
changes  it  must  undergo  in  order  to  gain  the  desired  degree  of  hardness 
and  toughness.  We  do  not  yet  know  enough  about  the  pyro-chemical 
behavior  of  clay  to  enable  us  to  answer  either  of  these  questions  with 
confidence. 

36 


ROLFE.]  DISTRIBUTION    OF    PAVING    BRICK    MATERIAL.  37 

We  know,  or  think  we  know,  that  vitrification  tends  to  harden  the 
brick  and  that  proper  regulation  of  the  rate  of  cooling  tends  to  make  it 
tough.  We  also  think  we  know  that  a  mixture  of  ingredients  which 
fuse  at  different  temperatures  is  better  than  a  mass  of  uniform  com- 
position, and  that  if  the  mixture  while  possessing  the  necessary  degree 
of  plasticity  has  its  grains  so  firmly  cemented  that  they  will  go  through 
the  processes  of  preparation  and  reach  the  molding  machines  as  a  mix- 
ture of  particles  varying  in  size  from  coarse  to  very  fine  it  will  enable  us 
to  reach  the  desired  result  more  cheaply  than  would  otherwise  be 
possible. 

In  consequence  of  this  we  naturally  look  for  an  impure  shale  as  the 
most  available  material  for  the  manufacture  of  pavers,  first,  because  the 
impurities  it  contains  will  probably  give  us  the  desired  range  in  fusi- 
bility, and  second,  because  shale  after  all  is  nothing  but  clay  whose 
particles  have  been  cemented  and  which  by  careful  crushing  can  be 
converted  into  a  mass  which  while  having  the  necessary  plasticity,  will 
at  the  same  time  contain  grains  varying  widely  in  size  and  density.  In 
consequence  of  this  many  people  have  come  to  believe  that  shales  furnish 
the  only  available  material  from  which  pavers  can  be  made,  and  that 
shales  from  the  coal  measures  are  much  more  likely  to  make  good  pavers 
than  those  from  any  other  horizon. 

This  opinion  seems  not  to  be  well  founded,  for  there  is  no  good  reason 
why  coal  measure  shales  should  differ  in  any  way  from  those  of  any 
other  age.  It  seems  to  be  true  that  the  period  of  the  coal  measures 
was  one  of  unusual  instability,  and  that  the  frequent  changes  in  condi- 
tions brought  corresponding  changes  in  the  character  of  the  sediments 
which  were  deposited  at  a  given  point,  so  that  the  content  of  sand  in 
the  coal  measure  shales  varies  more  widely  than  is  usual,  and  this  in 
connection  with  the  frequent  occurrence  of  beds  of  coal  at  the  base 
of  the  shale  may  account  for  the  popular  prejudice. 

It  is  true,  however,  that  some  of  the  very  best  pavers  are  manufactured 
from  clays  of  other  ages  and  recent  investigations  seem  to  indicate  that 
most,  if  not  all,  clays  when  properly  handled,  can  be  made  into  pavers 
of  excellent  quality.  The  Holland  and  Oldenburg  clinkers,  excellent 
pavers,  are  made  from  glacial  clays. 

What  is  Vitrification  ? — It  is  well  known  that  clay  as  it  comes  from  the 
machine  contains  a  greater  or  less,  but  always  a  considerable,  proportion 
of  mechanical  water,  and  that  if  the  clay  has  been  properly  prepared  this 
will  all  pass  off  in  the  dryer  or  during  the  first  water-smoking  without 
inducing  any  chemical  change  whatever.  We  also  know  that  it  contains 
•a  considerable  percentage  of  combined  water  or  water  of  hydration  which 
is  driven  off  during  the  second  water-smoking,  and  that  this  process  leaves 
the  clay  anhydrous,  nonplastic,  and  incapable  of  recovering  these 
properties  by  any  known  process.  It  is  also  known  that  after  the  clay 
has  lost  its  water,  if  the  temperature  of  the  kiln  is  sufficiently  high,  it 
will  shrink  slightly,  become  less  porous,  and  change  its  structure  en- 
tirely. Instead  of  the  granular  or  but  loosely  coherent  structure  shown 
by  the  surface  of  fracture  immediately  after  the  conclusion  of  the  water- 
smoking  process,  we  now  have  a  compact  glassy  or  felsitic,  all  but  im- 
pervious, substance  which  plainly  indicates  that  the  body  has  undergone 


38  PAVING   BRICK    AND    PAVING    BRICK   CLAYS.  Tbull.  no.  9 

profound  chemical  changes  that  have  transformed  it  from  an  earthy  into 
a  stony  material.  It  is  to  the  sum  of  these  changes  that  we  apply  the 
term  vitrification. 

We  do  not  yet  fully  understand  their  nature,  but  we  think  we  know 
some  things  about  them.  We  believe  that  the  increasing  temperature  of 
the  kiln  induces  chemical  changes  and  solid  solutions  in  the  clay  in 
virtue  of  which  more  easily  fusible  compounds  and  mixtures  are  formed ; 
that  when  these  compounds  reach  incipient  or  actual  fusion  they  induce 
similar  changes  in  other  ingredients  of  the  clay  which  would  not  undergo 
chemical  transformation  at  that  temperature  if  it  were  not  for  the  pres- 
ence of  the  first  formed  compounds.  When  these  last  compounds  reach 
partial  or  complete  fusion  they  react  on  yet  more  refractory  ingredients 
of  the  clay,  and  so  on. 

When  fusion  occurs  in  these  compounds  they  increase  in  volume  and 
become  slightly  blebby,  they  also  tend  to  settle  together,  and  by  a  com- 
bination of  these  two  processes  the  pores  are  filled,  the  structure  becomes 
more  impervious,  and  the  material  harder. 

Distinction  between  vitrifaction  and  fusion. — If  a  mass  made  up  of  a 
single  chemical  compound,  like  pure  kaolin  or  any  one  of  the  group  of 
similar  substances  which  are  found  in  clay,  be  ground  to  uniform  fine- 
ness, moulded,  dried,  and  gradually  heated,  it  will  pass  through  all  the 
changes  enumerated  above;  but  as  all  the  particles  are  of  like  size  and 
have  the  same  composition  each  will  be  affected  in  the  same  way  by  heat, 
and,  consequently,  each  will  pass  into  incipient  fusion  at  the  same  tem- 
perature so  that  the  whole  mass  will  soften  at  approximately  the  same 
time  and  become  deformed.  In  such  a  mass  the  temperature  of  vitrifac- 
tion and  that  of  fusion  will  usually  be  so  close  together  that  it  will  be 
difficult  so  to  control  the  fires  as  to  produce  complete  vitrifaction  without 
deformation  of  the  brick. 

On  the  other  hand,  if,  as  is  usually  the  case  with  clays,  the  mass  is 
made  up  of  several  compounds  each  having  a  different  fusion  point  and 
which  are  also  capable  of  uniting  at  certain  temperatures  to  form  new 
compounds  which  have  yet  other  fusing  points,  the  temperature  at  which 
incipient  fusion  or  vitrifaction  begins  and  that  at  which  the  whole  mass 
softens  may  be  widely  different,  and  will  usually  be  more  widely  separ- 
ated than  is  the  case  with  a  pure  substance. 

Again,  if  the  original  mass  contained  both  coarse  and  fine  particles  the 
finer  particles  will  be  first  attacked,  then  those  which  are  coarser  and  so 
on  until  the  largest  are  involved  and  in  this  way  the  range  of  vitrifaction 
will  be  widened. 

Conditions  which  ore  essential  in  a  paving  brick  clay. — From  what  has 
preceded  we  can  see  that  a  clay  from  which  paving  brick  are  to  be  man- 
ufactured  must  be  a  mixture  of  more  and  less  fusible  materials,  the 
more  refractory  particles  forming  a  skeleton  which  holds  the  mass  in 
shape,  while  the  more  readily  vitrifiable  portions  undergo  chemical 
changes,  form  solid  solutions,  become  vesicular,  and  draw  together  until 
the  pore  spaces  are  partially  or  wholly  filled  and  the  mass  becomes 
relatively  impervious. 

The  skeleton  spoken  of  above  may  be  composed  of  more  refractory 
material  than  the  remainder  of  the  brick  or  may  simply  be  made  up  of 


ROLFE.]  DISTRIBUTION    OF    PAVING    BRICK    MATERIAL.  39 

coarser  particles  of  the  Bame  materia]  as  the  rest,  but  in  the  latter  case 
the  range  of  vitrifaction  would  usually  not  bo  very  wide. 

If  a  given  clay  does  not  fulfill  the  conditions  named  above  the  defect 
musl  be  remedied  by  mixing  it  thoroughly  with  more  or  less  refractory 

material  or  by  coarser  or  filer  -rinding  of  a  portion,  as  the  case  may 
demand. 

If  ,i  clay  does  fulfill  the  conditions  in  a  measure,  but  the  range  of  vitri- 
faction is  narrow,  this  may  often  be  remedied  by  proper  mixing  or 
handling. 

If  all  or  a  large  proportion  of  the  particles  are  so  very  fine  that  the 
clay  settles  into  a  compact,  almost  impervious  mass  so  that  it  is  difficult 
to  dry  and  cracks  badly,  some  coarser  material  must  be  introduced  or 
-nine  method  of  handling  devised  to  open  the  structure  of  the  mass  and 
allow  the  water  to  pass  out  readily.  When,  as  is  not  infrequently  the 
case,  this  tine-grained,  compact  mass  shows  a  decided  tendency  to  split 
up  into  cubes  instead  of  disintegrating  under  the  treatment  ordinarily 
given  to  clays,  some  special  plan  such  as  mixing  into  a  thin  paste  with 
water  and  allowing  it  to  settle,  or  more  thorough  grinding  and  mixing 
than  is  usually  resorted  to  will  have  to  form  part  of  the  preparation  in 
order  that  the  coarser  material  may  be  thoroughly  incorporated,  or,  ex- 
posing the  clay  to  frost  during  the  winter  must  be  resorted  to  in  order 
to  break  up  the  strong  tendency  to  joint.  Experience  has  shown  that  this 
tendency  can  be  overcome  by  any  of  the  methods  mentioned,  but  as  they 
are  all  too  expensive  to  be  used  in  general  practice,  some  other  plan  of 
handling  these  clays  must  be  devised.* 

Xo  attempt  has  been  made  in  the  foregoing  paragraphs  to  enumerate 
all  the  difficulties  that  may  arise  in  the  preparation  of  materials  for  the 
manufacture  of  paving  brick,  but  perhaps  we  have  gone  far  enough  to 
indicate  what  was  meant  by  the  claim  that  pavers  of  excellent  quality 
may  be  made  from  clays  which  are  not  now  considered  available,  if 
proper  admixtures  are  made  and  the  materials  are  correctly  handled. 
Whether  it  will  pay  to  do  these  things  on  a  commercial  basis  is  a  matter 
which  local  conditions  alone  can  decide  in  each  case. 

I  repeat  at  this  point  what  I  said  earlier  in  this  section.  We  know- 
Aery  little  about  details  in  the  pyro-chemical  behavior  of  clays.  It  is  a 
matter  which  we  hope  to  see  taken  up  in  the  near  future  and  when  this 
is  done  I  have  no  doubt  that  many  of  the  things  we  now  think  we  know 
will  have  to  be  modified,  but  although  this  is  true,  such  an  investigation 
should  point  the  way  to  the  solution  of  many  of  the  problems  which  now 
disturb  us. 

In  the  foregoing  pages  I  have  tried  to  show  that  in  the  present  state  of 
our  knowledge  it  is  impossible  to  answer  the  question  "'what  is  a  paving 
brick  clay?'7  I  have  endeavored  to  show  that  no  special  kind  of  clay 
is  required  for  the  manufacture  of  pavers,  but  its  fitness  for  such  us 
more  a  question  of  physical  structure  than  of  chemical  composition  :  at  the 
same  time  it  must  be  realized  that  certain  mineral  substances  when 
present  in  largeT  quantities  unfit  a  clay  for  this  purpose.  I  have  also 
tried  to  suggest  the  possibility  (which  we  know  in  certain  cases  to  be  a 
fact)   that,  while  suitable  structure  has  been  given  to  certain  shales  by 


This  has  now  been  done,  and  the  method  will  be  described  in  a  later  bulletin. 


40  PAVING    BRICK    AND    PAVING   BRICK   CLAYS.  [bull.  no.  9 

nature,  we  may  devise  ways  by  which  this  lack  of  structure  may  be  com- 
pensated in  clays  that  do  not  now  possess  it,  using  means  so  inexpensive 
as  to  make  the  operations  commercially  successful. 

We  are  now  in  a  position  to  hurriedly  trace  the  geological  history  of 
our  State  with  a  view  to  ascertaining  where  deposits  of  those  materials 
which  are  most  likely  to  be  useful  to  the  manufacturer  of  vitrified  brick 
may  be  found.  We  hope  the  time  will  come  when  we  can  speak  definitely 
of  the  properties  of  these  deposits,  but  until  a  survey  of  the  clays  of 
our  State,  such  as  is  now  in  progress  in  Ohio,  shall  be  made,  we  must 
content  ourselves  with  indicating  where  suitable  deposits  are  likely  to 
he  found. 

Geology  of  Clays. 

origin. 

The  origin  of  clays  has  been  discussed  at  length  in  the  section  on  the 
geology  of  clays.  It  is  there  shown  that  primarily  all  clays  come 
from  the  decomposition  of  crystalline  rocks;  that  often  these  clays  re- 
main as  a  mantle  more  or  less  thick  covering  the  undecomposed  portion 
of  the  rocks  from  which  they  were  derived,  but  that  more  frequently  they 
are  lifted  by  running  water  and  carried  to  some  more  or  less  distant 
point  and  there  assorted  and  deposited.  When  these  deposits  are  made 
at  the  border  of  the  ocean  the  clays  are  built  into  the  rocks  which  are 
always  forming  in  such  places.  Often  the  clays  are  deposited  without 
much  admixture  of  other  materials  and  are  afterward  consolidated  into 
shales,  but  more  often  they  are  mixed  in  greater  or  less  proportion  with 
materials  which  are  to  form  limestones  or  sandstones,  and  so  become  an 
integral  part  of  those  rocks.  As  soon  as  these  limestones,  sandstones,  and 
shales  have  been  elevated  into  dry  land  they  are  attacked  by  erosion  and 
undergo  decomposition.  The  altered  portions  of  sandstones  become  lay- 
ers of  sand  containing  more  or  less  clay.  In  the  case  of  limestones  much 
of  the  lime  is  dissolved  and  carried  away  bearing  a  layer  of  clay  which 
covers  the  undecomposed  rock,  while  the  shales  often  break  down  into 
beds  of  more  or  less  plastic  clay.  Here  again,  as  in  the  case  of  the  cry- 
stalline rocks,  the  greater  portion  of  the  clay  is  carried  away  to  be  re- 
deposited  as  beds  of  alluvial  clay. 

OUTLINE   OF    THE   GEOLOGICAL   HISTORY    OF    ILLINOIS.* 

General  Section. — The  geologist,  like  the  historian,  divides  the  history 
of  a  country  into  periods  which  are  separated  from  each  other  by  some 
noteworthy  change  either  in  the  structure  of  the  rocks  or  the  fossil  forms 
which  they  contain.  These  divisions  of  the  geologist  differ  from  those  of 
the  historian  in  that  each  covers  an  almost  inconceivably  long  period  of 
time,  and  that  in  that  there  is  no  sort  of  relation  between  them  as  to  the 


*A  brief  description  of  the  geology  of  the  State,  accompanied  by  a  geological 
map,  prepared  by  Stuart  Weller,  is  found  in  Bulletin  6  of  the  State  Geological 
Survey.  This  will  be  sent  for  45  cents  on  application  to  the  Director  State  Geolo- 
gical Survey,  Urbana,  111.  The  notes  given  here  are  intended  merely  to  bring  out 
the  facts  necessary  to  a  good  understanding  of  the  distribution  of  the  clay-bear- 
ing formations. 


ROLFE.] 


DISTRIBUTION   OF    PAVING    BBICK    MATERIAL. 


41 


length  of  time  which  each  covers,  the  divisions  of  time  represented  in 
the  history  of  Illinois  are  as  follows: 


I    Quaternary  or  Glacial  Period. 


Cenozoic 
Era.         1 


Represented    only    in  that  part  of  the  State  south 
Tertiary  -!      of    the  Ozark  ridge;  no    subdivisions    have     been 
(      distinguished. 

Mesozoic     \  Represented    in  the  same  area  as  the  Tertiary  and  has  not  been 


Era.  I        separated  from  it. 


Paleozoic 
Era. 


f  Coal  Measures 

or  Pennsylvanian 


Carboniferous 


{  Chester 
|  St.  Louis 


Lower  Carboniferous     \  Keokuk 
or  Mississippian  |  Burlington 

^  Kinderhook 


Devonian 


Upper 
Middle 
Lower 


Silurian-Niagara 


Ordovician 


Trenton 


\  Cincinnatian 
(  Galena-Trenton 


r,        ,.        \  St.    Peters 
Canadian  j  Lower  Magnesian 


^  Cambrian-Potsdam. 


CAMBRIAN. 

Potsdam. — At  the  beginning  of  Potsdam  time  the  entire  area  of  this 
State  was  covered  by  the  waters  of  a  shallow  sea,  which  gradually  deep- 
ened until  the  close  of  the  period.  During  the  period  1,000  feet  or  more 
of  sandstones,  limestones,  and  shales  were  deposited.  The  rocks  of 
Potsdam  age  do  not  appear  at  the  surface  at  any  point  in  Illinois,  but 
do  outcrop  in  southern  Wisconsin.  They  are  believed  to  underlie  the 
entire  State,  and  form  our  deepest  source  of  artesian  water. 


ORDOVICIAN. 

Lowe?-  Magnesian. — At  the  close  of  the  Potsdam  the  condition  of  the 
sea  had  beconie  such  that  lime-secreting  animals  could  grow  in  abund- 
ance, but  the  waters  were  not  completely  or  continuously  clear.  During 
this  time  100  to  500  feet  of  a  strongly  argillaceous  limestone  was  de- 
posited over  the  entire  area  of  the  State.  Its  presence  has  not  been  actu- 
ally demonstrated  in  the  extreme  southern  portion,  but  there  is  every 
reason  to  believe  it  is  there.  It  appears  at  the  surface  only  in  LaSalle, 
Ogle  and  Calhoun  counties.  Near  Utica,  in  LaSalle  county,  it  is  used 
in  the  manufacture  of  hydraulic  cement. 

St.  Peters. — After  a  geologically  brief  but  really  long  period  following 
the  deposition  of  the  Lower  Magnesian,  during  which  northern  Illinois 


42  PAVING    BRICK   AND    PAVING    BRICK   CLAYS.  [bull.  no.  9 

was  dry  land,  the  State  was  again  covered  by  a  shallow  sea  and  about  150 
feet  of  a  characteristic  white  sand  was  deposited.  This  material  is 
much  used  in  the  manufacture  of  glass  and  forms,  above  the  Potsdam, 
the  principal  source  of  artesian  water  in  the  northern  portion  of  the 
state.  It  appears  at  the  surface  in  the  lower  ten  miles  of  the  valley  of 
Fox  river,  and  along  the  Illinois  from  Ottawa  almost  to  LaSalle;  also 
in  the  valley  of  Bock  river  from  north  of  Oregon  almost  to  Dixon  and 
at  Cap-a-Gres  near  the  southern  end  of  Calhoun  county. 

Galena-Trenton. — Following  the  period  of  deposition  of  the  St.  Peters, 
the  sea  became  again  suited  to  an  abundant  growth  of  organisms,  al- 
though the  waters  still  contained  considerable  quantities  of  clayey  sedi- 
ment. During  this  period  300  to  -100  feet  or  more  of  dolomite  and 
limestone  were  formed.  This  formation  carries  the  lead  and  zinc  -de- 
posits of  the  northwestern  portion  of  the  State  and  corresponds  with  the 
oil-bearing  limestone  of  eastern  Ohio  and  Indiana.  While  usually  com- 
posed of  limestone,  the  formation  contains  pockets  of  shale  and  clay. 

Cincinnatian  or  Maquoketa. — At  the  close  of  the  Trenton  period  the 
seas  became  very  muddy,  but  with  clearer  patches  here  and  there  in 
which  lime  secreting  organisms  could  nourish.  During  this  period  50  to 
200  feet  of  shales  and  shaly  limestones  were  formed.  While  in  Illinois 
the  Cincinnatian  consists,  for  the  most  part,  of  argillaceous  limestones 
and  limy  shales,  where  it  outcrops  in  the  northern  part  of  the  State,  it 
contains  local  deposits  of  very  pure  shale. 

SILURIAN. 

Niagaran. — With  the  close  of  the  Cincinnatian  the  seas  became  clear 
again,  and  a  heavy  bed  of  limestone  200  to  300  feet  thick  was  deposited 
over  the  entire  area.  This  limestone  is  usually  strongly  magnesian  in 
the  northern  and  central  portions,  calcareous  in  the  southern.  It  usually 
furnishes  building  stone  of  excellent  quality. 

It  has  usually  been  assumed  that  at  the  close  of  the  Silurian  the 
whole  of  the  northern  part  of  the  State  to  the  latitude  of  LaSalle  was 
elevated  above  the  seas  forming  the  first  permanent  land  within  its 
borders.  Only  scattered  Devonian  and  other  rocks  have  been  found  in 
this  portion  of  the  State  except  on  a  narrow  strip  along  its  southern  bor- 
der. Erosion  has  taken  place  to  such  an  extent  as  entirely  to  remove  to 
the  Silurian  from  one-half  of  the  area  and  the  Cincinnatian  from  at  least 
one-third,  leaving  the  Galena-Trenton  as  the  surface  rock  over  the  greater 
portion  of  the  northwestern  counties, 

DEVONIAN. 

The  Devonian  rocks  offer  little  that  is  of  practical  interest  in  this 
connection.  They  outcrop  at  only  three  or  four  points  in  the  State  and 
form  the  surface  over  a  very  small  area.  At  their  outcrops,  as  at'  the 
points  where  they  have  been  pierced  by  wells,  they  vary  from  10  to  150 
feet  in  thickness  divided  between  limestone  and  dark  shale.  '  Known 
facts  seem  to  indicate  that  the  Devonian  underlies  the  greater  portion  of 
the  State  south  of  the  latitude  of  LaSalle,  excepting  the  eastern  portions 
of  Will,  Kankakee,  and  Iroquois  counties. 


rolfe.]  DISTRIBUTION    OF    PAVING    BRICK    MATERIAL.  43 

CARBONIFEROUS. 

Mississippian  or  Lower  Carboniferous. — At  the  close  of  the  Devonian 
that  portion  of  the  State  south  of  the  latitude  named  received  a  heavy 
deposit  of  limestones,  sandstones,  and  shales  aggregating  150  to  200 
feet  in  thickness,  called  the  Lower  Carboniferous  or  Mississippian  series. 
Worthen  divides  this  series  into  five  groups  as  follows:  Kinderhook, 
mostly  shales  and  limestones,  100  to  150  feet;  Burlington,  massive  lime- 
stone, usually  excellent  as  a  building  stone,  50  to  200  feet:  Keokuk,  mas- 
sive  limestone  below,  passing  into  shales  in  the  upper  portion,  150  feet; 
St.  Louis,  mostly  heavy  bedded  argillaceous  limestone,  100  to  200  feet 
thick,  passing  locally  into  shales  on  one  hand  and  a  fine  quality  of  oolite 
on  the  other,  and  Chester,  consisting  of  heavy  beds  of  sandstones  and 
limestones  with  some  shahs,  in  all  500  to  800  feet  thick. 

The  Lower  Carboniferous  forms  the  bluffs  of  the  Mississippi  and  a 
variable  belt  to  the  eastward  from  the  southern  portion  of  Mercer  county 
to  Alexander  county  and  a  considerable  part  of  the  Ozark  ridge  across 
the  State.  It  is  believed  to  underlie  all  the  central  and  southern  part  of 
the  State,  and  well  records  indicate  that  it  increases  in  thickness  and  be- 
comes more  shaly  towards  the  eastern  border.  Present  information  seems 
to  indicate  that  the  Chester  does  not  occur  north  of  a  line  drawn  through 
Litchfield  and  Danville. 

Pennsylvaman  or  Coal  Measures. — For  a  long  time  subsequent  to  the 
deposition  of  the  Lower  Carboniferous,  that  portion  of  the  State  between 
the  latitudes  of  La  Salle  and  Carbondale  oscillated  between  a  slightly  ele- 
vated condition,  in  which  extensive  marshes  and  lakes  were  interspersed 
between  areas  of  higher  drier  land,  and  a  condition  in  which  the  entire 
area  was  covered  by  the  waters  of  a  shallow  sea  in  which  beds  of  shale 
and  sandstone  20  to  200  feet  thick  and  occasional  thin  beds  of  limestone 
accumulated.  These  conditions  alternated  many  times  with  the  result 
that  a  formation  now  50  to  1200  feet  thick  was  built  up  in  this  portion 
of  the  State.  In  the  marshes  and  lakes  great  beds  of  vegetable  matter 
accumulated,  which  were  afterward  converted  by  the  pressure  of  subse- 
quent deposits  into  bituminous  coal,  and  beds  of  this  material  are  now 
found  intercalated  in  the  sandstones  and  shales  before  mentioned. 

CRETACEOUS  AND  TERTIARY. 

After  the  uplift  that  marked  the  close  of  coal  measure  deposition  no 
portion  of  the  State  north  of  the  Ozarks  is  known  ever  to  have  beneath 
the  waters  of  the  ocean,  but  south  of  the  ridge  thick  deposits  of  sand- 
stones, limestones,  and  shales  were  laid  down.  These  deposits  have  not 
i  studied  with  sufficient  care  to  make  their  differentiation  possible, 
so  that  we  need  do  little  more  in  this  connection  than  point  out  their 
presence. 

PLEISTOCENE. 

Glacial  Deposits. — After  the  close  of  the  Tertiary  the  entire  surface  of 
the  State  north  of  the  Ozarks  except  small  portions  at  the  northwestern 
corner,  and  in  Calhoun  county,  was  covered  with  a  -beet  of  ice  of  great 


44  PAVING   BKICK   AND    PAVING   BRICK   CLAYS.  [bull.  no.  9 

thickness.  This  ice  sheet  came  to  us  from  the  regions  southwest  and 
southeast  of  Hudson's  Bay,  and  on  its  way  picked  up  the  soils  and 
loosened  fragments  of  rocks  which  had  been  accumulating  over  that  re- 
gion for  hundreds  of  thousands  of  years.  When  the  ice  melted  these  ma-- 
terials  were  deposited  over  the  surface  of  Illinois,  making  a  layer  which 
varies  greatly  in  thickness  but  will  probably  average  50  to  100  feet. 
This  is  known  as  boulder  or  glacial  clay.  Three  ice  sheets  separated  by 
long  intervals  are  supposed  to  have  covered  portions  of  Illinois.  The 
first  Illinois  Glacier  extended  as  far  south  as  the  latitude  of  Carbondale, 
and  when  it  disappeared  left  a  thick  deposit  of  glacial  clay.  The  sec- 
ond, or  lowan  Glacier,  extended  but  a  short  distance  below  the  northern 
boundary.  We  do  not  yet  know  the  exact  limits  of  the  territory  which  it 
covered.  The  third,  or  Wisconsin  Glacier,  covered  an  area  in  the  north- 
eastern portion  of  the  State  which  averages  about  90  miles  east  and  west 
by  about  200  north  and  south.  Its  boundaries  are  marked  by  a  prom- 
inent ridge  or  moraine  which  passes  near  Charleston,  Shelbyville,  De- 
catur, Peoria,  Princeton,  Eochelle,  Woodstock,  and  Harvard. 

Each  of  these  ice  sheets  left  its  deposit  of  boulder  clay,  and  as  we  dig 
through  the  deposits  the  upper  surface  of  each  is  marked  by  one  or  more 
of  the  following  characteristics,  yellow  clay,  black  earth,  pieces  of  wood, 
gas,  or  large  water-bearing  gravel  beds. 

AREAL  DISTRIBUTION. 

Keeping  in  mind  the  brief  descriptions  of  the  foregoing  paragraphs, 
we  may  now  divide  the  State  into  the  following  geological  areas,  Ordovi- 
cian,  Silurian,  Devonian,  Lower  Carboniferous,  Coal  Measures,  and  Cre- 
taceous or  Tertiary. 

Ordovician. — This  area  is  roughly  bounded  by  the  parallel  41  30'  and 
the  meridian  88  36',  covering  the  northeastern  part  of  the  State,  together 
with  a  narrow  strip  running  southward  through  western  Will,  Kankakee, 
Iroquois,  and  Ford  counties.  The  Galena-Trenton  now  forms  the  sur- 
face over  the  greater  part  of  this  area,  but  when  it  first  became  dry  land 
it  was  also  covered  by  the  Cincinnatian  and  Magaran.  These  have 
been  removed  from  most  of  the  area  by  erosion,  but  remnants  of  them 
still  remains  as  mounds  and  elevated  table  lands.  The  lowermost  beds 
of  the  Galena-Trenton  include  highly  argillaceous  limestones,  and  when- 
ever the  formation  has  been  long  exposed  to  the  action  of  the  weather 
the  lime  has  been  dissolved  and  carried  away  in  solution,  leaving  the  dis- 
seminated clay  as  a  mass  of  loose  material.  Where  this  is  not  exposed 
to  the  action  of  running  water,  it  has  accumulated  in  beds  or  pockets 
which  sometimes  cover  a  considerable  area.  Considerable  deposits  hav- 
ing this  origin  are  known  to  exist  in  the  area,  but  their  availability  for 
the  manufacture  of  pavers  has  never  been  tested  so  far  as  the  writer 
knows. 

In  all  the  mounds  and  table  lands  referred  to  above  the  Cincinnatian 
or  Maquoketa  comes  to  the  surface,  either  forming  the  apex  of  the  eleva- 
tion or  lying  immediately  beneath  a  capping  of  Niagaran.  This  Cincin- 
natian usually  appears  in  this  part  of  the  State  as  a  thin  bedded  limestone 
which  carries  a  large  percentage  of  clay,  but  locally  it  becomes  a  pure 


rolfe]  DISTRIBUTION   OF    PAVING   BRICK   MATERIAL.  45 

shale,  often  high  in  lime,  but  occasionally  almost  lime  free,  in  which 
case  it  becomes  a  promising  source  of  paving  material  (See  H  18  and 
H  21.)  The  Cincinnatian  also  outcrops  as  shale  near  Wilmington,  Will 
county.  A  considerable  percentage  of  the  Ordovician  area  is  covered 
with  glacial  deposits,  some  of  which  may  be  found  to  be  suited  to  the 
manufacture  of  pavers.  Small  areas  of  rocks  of  this  age  may  also  be 
found  near  Batchtown,  Calhoun  county;  Valmeyer,  Monroe  county;  and 
Thebes,  Alexander  county.  In  some  of  these  the  rocks  are  shaly  and  look 
promising  but  have  not  been  tested. 

Silurian. — This  formation  covers  the  greater  part  of  McHenry,  Lake, 
Cook,  Dupage,  Kane,  Will,  Kankakee,  and  Iroquois  counties,  and  small 
portions  of  Boone  and  DeKalb,  all  lying  in  the  northeastern  corner  of  the 
State.  The  surface  rock  is  the  massive  Niagarean  limestone  which  fur- 
nishes no  deposits  of  clay  or  shales  in  this  State.  It  is  everywhere  over- 
laid by  thick  deposits  of  glacial  drift  which  permit  the  underlying  rock 
to  appear  at  the  surface  in  small  areas  only. 

The  glacial  clays  of  this  area  present  the  wide  range  in  composition 
and  properties  so  characteristic  of  deposits  of  that  age.  No  studies  of 
these  clays  have  been  made  so  far  as  the  writer  knows,  but  he  feels  certain 
that  some  of  them  would  make  pavers  of  excellent  quality  if  properly 
treated. 

Small  areas  of  this  age  are  also  found  at  the  mouth  of  the  Illinois  and 
east  of  Thebes  in  Alexander  county,  but  they  afford  no  clays  or  shales. 

Devonian. — The  outcrops  of  Devonian  rocks  in  Illinois  are  of  small 
area  and  are  confined  to  three  localities,  viz. :  near  Eock  Island,  on 
either  side  of  the  Illinois  river  near  its  mouth,  and  near  Jonesboro  in 
Union  and  Alexander  counties.  In  all  these  areas  shales  are  to  be  found 
which  may  prove  valuable  as  paving  brick  material,  but  they  have  not 
been  tested. 

Lower  Carboniferous  or  Mississippian. — The  rocks  of  this  area  form 
a  broad,  but  very  irregular  belt,  along  the  Mississippi  from  New  Boston, 
Mercer  county,  to  the  southern  line  of  Union  county  and  thence  east 
across  the  state,  forming  the  Ozark  Eidge. 

Most  of  the  rocks  of  this  age  outcropping  in  the  area  described  are 
limestones  or  sandstones,  but  nearly  all  the  layers  pass  locally  into  shales, 
some  of  which,  notably  those  of  the  Kinderhook  and  St.  Louis,  have  been 
proved  to  have  the  qualities  desired  in  paving  brick  material,  but  in 
only  one  locality,  and  that  from  the  Kinderhook,  so  far  as  the  writer 
knows,  have  they  actually  been  used  for  this  purpose. 

Coal  Measure  or  Pennsylvanian. — This  area  covers  all  that  part  of  the, 
State  lying  between  the  parallel  41  30'  and  the  Ozark  Eidge  except  those 
portions  included  in  the  Silurian  and  Lower  Carboniferous.  Over  all 
this  area  shales  and  fire  clays  are  abundant  along  the  banks  of  the 
streams.  Many  of  them  are  all  that  could  be  desired  as  material  for  the 
manufacture  of  pavers,  and  they  often  present  the  added  advantage  of 
being  underlaid  by  a  bed  of  coal  which  may  be  used  for  fuel,  thus  lessen- 
ing the  cost  of  production.  All  the  paving  brick  plants  now  operating  in 
the  State  use  these  shales  and  all  but  one  of  those  in  the  western  part  of 
Indiana. 


46  PAVING    BRICK    AND    PAVING    BRICK   CLAYS.  [BULL.   NO.  9 

This  area  is  everywhere  overlaid  by  a  deposit  of  glacial  drift  which  is 
often  from  50  to  300  feet  in  thickness,  and  it  is  only  when  this  has  been 
removed  by  erosion  that  the  Coal   Measure  shales  come  to  the  surface. 

These  glacial  clays  are  now  only  used  in  the  manufacture  of  drain 
tile  and  common  building  brick,  but  it  is  hoped  that  means  will  soon  be 
devised  which  will  make  their  use  in  the  manufacture  of  vitrified  ware 
of  good  quality  commercially  possible. 

Cretaceous  and  Tertiary. — This  area  lies  entirely  south  of  the  Ozark 
Eidge  and  includes  the  greater  part  of  Alexander,  Pulaski  and  Massac 
counties,  and  a  small  part  of  Pope.  Many  of  the  clay  deposits  of  this  area 
are  of  excellent  quality  and  the  tests  to  which  some  of  them  have  been 
subjected  indicate  that  they  would  make  excellent  pavers. 

It  is  thus  seen  that  there  are  no  larger  areas  within  the  boundaries  of 
the  State  that  do  not  contain  deposits  of  clay  which  are  at  least  promising 
as  sources  of  material  for  the  manufacture  of  pavers.  It  is  hoped  that 
in  the  near  future  the  survey  will  find  itself  in  a  position  to  demonstrate 
the  availability  of  these  deposits  for  this  use. 


QUALITIES  OF  HIGH  GRADE  PAVING  BRICK  AND  TESTS 
USED  IN  DETERMINING  THEM. 

[By  Arthur  N.   Talbot.] 


Introduction. 


The  extensive  use  of  brick  for  street  paving  purposes  makes  the 
formulation  of  the  qualities  requisite  for  a  good  paving  brick  a  matter 
of  importance  to  both  producer  and  consumer.  Although  it  may  not  be 
difficult  to  agree  on  these  qualities  in  the  abstract,  it  is  not  easy  to  ex- 
press the  requirements  in  definite  and  concrete  form  and  in  terms  accept- 
able to  both  manufacturer  and  municipality.  It  is  an  accepted  principle 
that  the  quality  of  an  engineering  material  should  not  be  left  merely  to 
the  judgment  of  an  individual,  no  matter  how  experienced  the  individual 
may  be;  recourse  should  be  had  to  physical  tests  and  these  should  be 
definite  and  discriminating.  Such  tests  may  not  of  themselves  be  con- 
clusive, the  results  are  in  the  nature  of  evidence  which  must  be  inter- 
preted and  judged  in  the  light  of  other  information.  Perfect  materials 
for  a  pavement  may  not  be  obtained  and  high  quality  usually  means 
increased  cost  of  production,  but  on  the  other  hand  the  additional  cost 
of  a  good  article  is  usually  made  up  many  times  over  in  the  increased 
length  of  life  and  improved  surface  of  the  pavement  as  compared  with  a 
pavement  in  which  an  inferior  brick  is  used.  The  problem  of  formu- 
lating requirements  and  making  tests  is  further  complicated  by  the  diffi- 
culties encountered  in  selecting  brick  for  test  and  comparison  from  the 
piles  of  brick  along  the  street  and  in  judging  whether  the  variation  from 
the  average  throughout  these  piles  is  sufficient  of  itself  to  be  cause  for  re- 
jection. Enough  has  been  said  to  justify  the  view  that  the  formulation 
of  the  qualities  needed  in  a  high  grade  paving  brick  and  the  use  and 
interpretation  of  physical  tests  for  determining  the  qualities  of  the  brick 
for  aiding  in  deciding  whether  brick  come  up  to  the  required  grade,  are 
matters  worthy  of  discussion  by  engineers  and  manufacturers.  A  general 
statement  of  matters  connected  with  brick  testing  may  be  of  advantage  to 
many  who  are  interested  in  the  construction  and  use  of  brick  pavement. 

Hosi  -pecifieations  for  materials  set  forth  qualities  of  materials  to  be 
furnished  by  the  producer  to  the  consumer.  In  the  case  of  brick  pave- 
ments the  producer  (i.  e.,  the  manufacturer)  and  the  consumer  (i.  e.,  the 
municipality  and  the  property  owner,  as  represented  by  the  municipal 
administrative  officers)  are  to  use  certain  requirements  to  define  the  ma- 
terial to  be  put  into  the  pavement.  Some  of  the  purposes  of  these  re- 
quirements and  tests  may  be  expressed  as  follows : 

1.  To  make  a  basis  or  definition  of  what  is  wanted  and  what  is  to  be 
furnished.  This  is  the  commonly  accepted  purpose  of  such  requirements  and 
tests. 

47 


48  PAVING    BRICK    AND    PAVING   BRICK   CLAYS.  [bull.  no.  9 

2.  To  enable  the  city  to  secure  material  which  will  be  as  serviceable  as 
other  material  which  has  passed  the  requirements  and  which  has  stood  the 
test  of  traffic  and  time.    This  makes  the  tests  in  a  sense  a  guaranty  of  quality. 

3.  To  enable  comparisons  to  be  made  between  the  products  offered..  It 
is  quite  possible  that  tests  may  show  that  a  given  brick  is  above  the  require- 
ments, or  that  a  slight  difference  in  price  is  made  up  many  times  by  the 
superior  quality  of  the  article. 

4.  To  improve  the  general  quality  of  the  product  put  on  the  market.  It 
has  frequently  happened  that  the  formulation  of  requirements  and  the  care- 
ful inspection  of  the  articles  offered  have  resulted  in  improved  quality  and 
this  in  many  cases  even  without  increasing  the  cost  of  production.  The 
manufacturer  has  been  stimulated  thereby  to  study  the  process  of  production 
and  to  seek  to  improve  methods  of  manufacture  and  quality  of  product.  One 
need  instance  only  structural  steel  and  paints  and  oils  to  show  improve- 
ments in  quality  following  carefully  made  requirements  and  tests  to  show 
the  beneficial  influence  of  adequate  inspection  and  tests. 

5.  To  safeguard  the  interests  of  the  public  and  of  the  taxpayer.  The  Ilfi- 
nois  law  requires,  and  rightfully,  too,  that  the  nature  and  quality  of  the 
improvement  shall  be  explicitly  stated,  and  evidently  intends  that  the  tax- 
payer may  be  able  to  determine  (1)  what  the  improvement  is  to  be,  and  (2) 
whether  it  is  being  put  in  as  described. 

6.  In  the  occasional  cases  where  abuse  of  authority  or  improper  or  dis- 
honest construction  may  require  a  check,  to  enable  control  to  be  exercised 
over  incapable  or  dishonest  contractors  or  city  officials,  and  to  restrain  care- 
less or  inefficient  employes,  or  men  who  may  have  a  mistaken  notion  of  what 
their  employer's  interests  are. 

7.  To  educate  producer,  consumer,  and  their  agents  in  a  knowledge  of  the 
qualities  needed  in  paving  brick, — from  the  manufacturer  and  the  contractor 
and  their  employes  to  the  mayor,  the  engineer,  the  inspector,  and  the  prop- 
erty owner.  It  should  be  recognized  that  those  who  have  charge  of  munici- 
pal work  are  a  constantly  changing  class,  and  that  the  property  owner  may 
have  little  knowledge  of  pavement  construction. 

8.  Not  the  least  important  of  the  reasons  for  having  an  explicit  and  definite 
statement  of  the  qualities  and  requirements  for  a  paving  brick  is  to  give 
the  opportunity  for  all  bids  to  be  made  on  the  same  basis  and  for  the  bidder 
to  fix  his  price  according  to  the  quality  of  the  article  wanted  and  thus  to 
facilitate  fair  competition. 

It  is  evident  that  a  knowledge  of  the  qualities  of  a  high-grade  pav- 
ing brick  and  of  the  defects  to  be  avoided  in  the  selection  of  brick  will 
be  useful  in  making  up  the  requirements  defining  the  grade  of  brick  to 
be  used  and  that  the  method  of  making  tests  .ought  to  be  studied  both  in 
relation  to  the  wear  of  the  brick  in  the  street  and  to  the  bearing  of  the 
results  of  the  physical  tests  upon  the  wearing  and  other  qualities  of  the 
brick.  In  this  article  a  discussion  of  the  qualities  needed  in  a  paving 
brick  will  be  given  first,  and  the  bearing  of  the  tests  upon  these  qualities 
will  then  be  taken  up,  though  it  will  be  seen  that  the  relation  between 
the  method  of  testing  and  the  quality  to  be  determined  is  so  intimate 
that  their  discussion  must  be  carried  on  together  to  a  considerable  extent. 

QUALITIES  FOR  A  HIGH  GRADE  PAVING  BRICK. 

General. — Paving  brick  should  possess  the  following  qualities :  1, 
Toughness,  hardness,  and  strength.  2.  Uniformity  of  quality  through- 
out a  given  lot  of  brick.  3.  Homogeneity  of  structure  and  freedom 
from  laminations.  4.  Weather-resisting  quality.  5.  Eegularity  in 
form  and  size.    These  qualities  are  named  somewhat  in  the  order  of  their 


talbot]  QUALITIES   OF    HIGH    GRADE    PAVING    BRICK.  49 

importance,  though  it  should  be  recognized  that  several  of  them  are 
mutually  inclusive. 

1.  Toughness,  Hardness,  and  Strength. — Toughness  is  that  property 
•  if  a  material  which  indicates  its  ability  to  withstand  destruction  by  shock 
or  impact  or  by  a  marked  distortion  of  the  form  of  the  piece.  It  is  the 
opposite  of  brittleness.  Of  course  toughness  differs  in  different  ma- 
terials, and  it  varies  in  a  given  material.  Mild  steel  has  the  property  of 
toughness  to  a  marked  degree  and  will  withstand  distortion  and  abuse. 
One  test  of  the  toughness  of  a  specimen  of  mild  steel  is  to  bend  the  piece 
cold  180°  flat  on  itself  without  sign  of  fracture.  Cast  iron  is  a  more  brit- 
tle material  and  ordinarily  is  not  used  to  take  shock  except  in  large  masses 
and  at  low  strvsses.  Different  grades  of  cast  iron,  however,  possess  differ- 
(  i  degrees  of  toughness,  and  a  good  quality  of  cast  iron  will  bend  consid- 
erably before  rupturing.  With  such  materials  the  physical  property  of 
toughing  which  will  permit  bending  and  distortion  in  relatively  thin 
pieces  will  give  ability  to  withstand  blows  and  the  sudden  application 
of  loads  in  thicker  masses,  In  the  case  of  paving  brick,  a  lack  of  tough- 
ness causes  the  brick  to  chip  and  spall  under  the  action  of  horses'  hoofs 
and  not  to  resist  blows  and  abuse  under  the  action  of  traffic.  This  ele- 
ment of  toughness  is  one  of  the  most  important  qualities  in  a  good  paver. 

Hardness  is  that  property  of  a  material  which  indicates  its  ability  to 
resist  abrasion.  The  necessity  for  hardness  is  self-evident.  The  grinding 
action  of  loaded  wheels  sliding  sidewise  or  even  rolling  forward  wears 
away  the  surface  of  the  brick  and  forms  grit  or  dust.  This  abrasion  is 
the  principal  source  of  wear  in  a  well-constructed  pavement  made  of  a 
good  quality  of  brick.  Soft  brick  will  wear  rapidly  under  the  action  of 
traffic.  Hardness  is  therefore  a  desirable  property  for  paving  brick  to 
possess. 

Strength  is  another  important  element.  The  loads  of  wheels  are  con- 
centrated on  a  small  area,  possibly  a  ton  on  a  fraction  of  a  square  inch. 
With  an  uneven  bedding  of  a  brick  or  other  conditions  like  its  being  sup- 
ported on  a  pebble  or  by  an  adjoining  brick,  considerable  flexural  action 
is  developed,  and  even  twisting  action,  and  the  brick  acts  as  a  beam. 
With  uneven  surfaces  there  may  be  considerable  horizontal  thrust.  It  has 
been  argued  that  lack  of  strength  in  the  brick  does  not  seriously  affect 
brick  pavements  and  that  pavements  do  not  fail  from  this  source,  but  the 
writer  lias  seen  brick  of  a  mediocre  quality  spall  under  the  trust  of  a 
loaded  wheel  again  and  again,  and  it  is  not  uncommon  to  see  brick  broken 
in  two  by  the  passage  of  loaded  wagons.  Moreover,  when  a  material  is 
otherwise  severely  strained  the  effect  of  abrasion  and  impact  is  greater, 
and  the  brick  which  under  heavy  stresses  remains  well  b?low  its  ultimate 
strength  will  be  better  able  to  withstand  the  abrasive  action  which  takes 
place  under  such  conditions.  Besides,  high  compressive  strength  is  gen- 
erally conducive  to  hardness,  and  for  granular  materials  a  relatively  high 
tensile  strength  such  as  accompanies  high  values  in  cross  breaking  is  an 
indication  of  toughness  and  high  resilience  in  the  material. 

The  elements  of  toughness,  hardness,  and  strength  are  difficult  to 
differentiate,  since  one  involves  the  other.     On  the  other  hand,  a  very 

—4  G 


50  PAVING   BRICK   AND    PAVING   BRICK   CLAYS.  [bull.  no.  9 

hard  brick  may  be  quite  brittle,  so  much  so  as  to  be  an  inferior  article. 
Some  very  tough  bricks  are  not  hard  enough  to  resist  abrasive  action 
sufficiently.  Where  this  is  so,  there  may  be  some  defect  in  the  process 
or  treatment  during  manufacture.  Generally  flexural  strength  goes  with 
toughness  and  compressive  strength  with  hardness.  Not  all  these  qual- 
ities may  be  expected  to  exist  to  the  same  degree  in  brick  of  different 
makes,  and  hence  the  different  properties  should  be  considered  in  discuss- 
ing the  merits  of  a  variety  of  brick. 

2.  Uniformity  of  Quality. — In  the  enumeration  of  properties  needed 
in  a  paving  brick,  uniformity  of  quality  throughout  a  given  lot  has  been 
placed  second  in  the  list,  and  it  is  believed  by  the  writer  that  it  is  hardly 
secondary  to  the  qualities  of  toughness,  hardness,  and  strength.  It  is 
highly  desirable  that  all  the  brick  in  a  given  lot  shall  be  as  nearly  uni- 
form in  make-up  as  is  practicable  with  the  best  materials  and  manufac- 
ture, and  especially  that  brick  which  will  be  near  each  other  shall  be  of 
uniform  quality.  If  one  brick  is  soft  and  the  next  one  hard,  an  uneven 
surface  will  be  produced  more  quickly  than  otherwise,  the  resulting  soft 
spots  receiving  harder  wear  as  the  low  spots  appear.  A  pavement  of  soft 
but  uniform  bricks  will  wear  away  at  a  uniform  rate,  and  its  surface  may 
remain  less  objectionable  than  one  containing  a  fair  proportion  of  harder 
brick.  The  products  of  some  plants  are  particularly  troublesome  in  this 
direction,  while  those  of  others  are  fairly  uniform.  This  quality  or  lack 
of  this  quality  renders  inspection  on  the  street  very  difficult,  and  has 
done  as  much  as  any  thing  to  throw  discredit  on  brick  pavement.  Brick 
manufacturers  will  render  service  to  their  industry  by  striving  to  secure 
greater  uniformity  and  municipalities  must,  on  their  part,  protect  their 
interests  by  holding  stricter  requirements  than  in  the  past.  The  import- 
ance of  uniformity  has  not  generally  been  sufficiently  recognized. 

3.  Homogeneity  of  Structure  and  Freedom  from  Laminations. — 
Homogeneity  of  structure  gives  uniformity  of  wear  throughout  the  brick 
and  adds  to  ability  to  resist  wear  and  breakage.  A  brick  of  homogeneous 
texture  is  more  likely  to  possess  toughness  and  strength  to  the  requisite 
degree  than  is  one  of  variable  texture.  Laminations  in  a  brick  are  par- 
ticularly objectionable,  since  they  markedly  decrease  toughness  and 
strength,  and  permit  chipping  and  spalling.  It  is  important  that  tests 
for  toughness,  hardness,  and  strength  be  made  in  such  a  way  as  to  bring 
out  the  effect  of  laminations  and  other  defects  which  may  not  be  apparent 
near  the  surface  of  the  brick.  The  brick  should  be  uniform  throughout, 
evenly  vitrified,  and  free  from  spots  which  result  from  imperfect  crush- 
ing and  mixing  of  materials  and  from  any  element  which  will  tend  to  dis- 
rupt the  brick  by  later  changes  in  condition. 

4.  Weather-resisting  Quality. — Strong,  tough,  hard  brick  of  low  poros- 
ity and  even  texture  are  not  injured  by  weather  changes.  Soft,  weak  and 
porous  brick  are  affected  by  frost  and  other  weather  conditions,  and  a 
laminated  and  coarse  structure  promotes  disintegration. 

Generally  speaking,  high  grade  paving  brick  are  of  sufficient  strength 
to  withstand  weather  influences,  but  the  combination  of  weather  effect 
and  traffic  is  more  noticeable.  The  writer  has  observed  the  spalling  and 
grinding  of  soft  brick  under  heavy  loads  during  the  time  when  they 
were  wet  and  frozen  on  pavement  where  the  wear  was  much  slower  under 


talbot]  QUALITIES   OF    HIGH    GRADE    PAVING    BRICK.  0± 

better  weather  conditions.  Occasionally  a  pavement  is  found  where 
rapid  deterioration  takes  place  during  the  early  spring.  Part  of  the 
trouble  of  this  sort  is  due  to  improper  bedding  and  filling. 

5.  Regularity  in  Form  and  Size. — Well-formed  brick  of  uniform 
size  give  a  smooth  and  regular  surface  to  the  pavement,  and  thus  add 
to  its  attractiveness.  Besides,  such  brick  will  have  uniform  bearing  and 
exert  even  pressure  on  the  sand  cushion  below,  and  thus  will  remain  in 
position  during  the  life  of  the  pavement.  Desirable  as  this  uniformity 
is,  it  does  not  pay  to  obtain  it  at  the  expense  of  the  wearing  qualities, 
and  pavements  with  the  smoothest  surfaces  do  not  always  give  the  best 
results.  Some  irregularity  in  shape  and  form  must  be  expected  and 
permitted,  especially  with  clays  of  a  certain  character.  No  general 
rule  may  be  formulated,  and  the  amount  of  irregularity  may  easily 
be  settled  upon  in  connection  with  any  given  lot  of  brick. 

Tests  For  Quality. 
general  statement. 

The  main  advantage  of  physical  tests  of  paving  brick  lies  in  giving 
definite  evidence  having  a  bearing  upon  the  properties  and  qualities 
of  the  brick.  To  make  this  evidence  useful,  the  relation  of  the  method 
of  making  the  tests  and  their  results  to  the  qualities  thereby  determined 
must  be  understood.  In  several  of  the  tests  numerical  standards  may 
be  set  for  general  use.  However,  in  many  cases  and  especially  for  some 
of  the  tests  which  may  be  made,  it  is  best  to  consider  that  the  results 
are  advisory  in  nature  and  that  hard  and  fast  limits  may  not  be  set. 
In  subsidiary  tests  the  results  may  give  evidence  which  confirms  find- 
ings otherwise  made  or  which  throws  light  upon  unsettled  questions  and 
aids  in  interpretation  of  data  obtained  by  other  tests. 

In  tests  of  materials  it  is  not  essential  that  the  material  shall  be 
subjected  to  the  same  action  in  the  process  of  testing  as  it  will  receive 
in  the  structure  in  which  it  is  to  be  placed.  The  cold  bend  test  of  steel 
is  one  of  the  most  useful  and  instructive  of  tests,  but  it  differs  radically 
from  any  condition  of  service  in  which  the  steel  will  be  placed.  The 
value  of  a  test  will  depend  upon  the  properties  determined,  and  the 
criterion  will  be,  does  the  test  establish  definitely  certain  properties  of 
the  material,  or  does  it  give  definite  evidence  concerning  specific  qual- 
ities, and  does  not  the  method  give  results  similar  to  those  found  in 
service.  Thus  the  ordinary  rattler  test  is  quite  unlike  the  action  of 
traffic  on  a  street,  but  if  it  determines  the  toughness  and  hardness  of 
a  brick  sufficiently  well  it  serves  its  purpose.  Because  high  grade 
paving  brick  do  not  crush  in  service  is  not  conclusive  evidence  that  the 
results  of  crushing  tests  do  not  give  important  information  concerning 
the  qualities  of  a  given  lot  of  brick.  Of  course,  a  test  which  approx- 
imates the  conditions  of  wear  and  stress  in  the  street  pavement  has  a 
distinct  advantage  in  that  it  appeals  to  the  lay  mind  and  gives  the  muni- 
cipal officer  .and  the  tax  payer  confidence  in  the  findings  which  would 
not  be  possible  in  a  test  of  seemingly  less  direct  applicability.  What- 
ever the  test,  its  purpose  and  the  bearing  of  the  results  on  the  qualities 
desired  in  the  brick  should  be  understood  and  accepted  by  all. 


52  PAVING    BRICK    AND    PAVING    BRICK   CLAYS.  [bull.  no.  9 

The  tests  which  have  been  used,  some  of  them  very  commonly,  others 
only  occasionally,  are:  1.  the  rattler  test  (called  also  the  impact  and 
abrasion  test);  2.  the  absorption  test;  3.  the  crushing  test;  4.  the 
cross-breaking  test;  5.  the  specific  gravity  test.  The  rattler  test  is 
commonly  considered  to  determine  toughness  and  hardness,  or  resist- 
ance to  impact  and  abrasion.  The  absorption  test  gives  information 
bearing  upon  the  degree  of  hardness  to  which  the  brick  has  been 
burned.  The  cross-breaking  test  and  the  crushing  test  determine 
strength  and  incidentally  give  evidence  of  the  hardness  and  toughness 
of  the  brick.  The  specific  gravity  test  must  be  classed  among  those 
tests  which  are  of  value  in  giving  general  information.  The  manner  of 
making  these  tests  will  now  be  described  and  some  discussion  given  of 
the  meaning  of  the  results  found  by  the  various  tests. 

THE  RATTLER   TEST. 

It  may  be  of  interest  to  recount  some  of  the  efforts  which  have  led 
up  to  the  present  standing  of  the  rattler  test.  During  the  earlier  years' 
experience  in  the  construction  of  brick  pavement  the  judgment  of  those 
in  charge  of  the  work  was  the  only  guide  used  when  passing  upon  the 
quality  of  paving  brick.  It  was  soon  seen  that  some  test  to  measure 
the  ability  of  a  brick  to  resist  wear  was  needed,  and  the  use  of  the 
foundry  rattler  or  tumbler,  employed  in  foundries  for  cleaning  castings, 
was  suggested.  Brick  were  placed  in  these  rattlers  with  a  charge  of 
foundry  shot,  which  is  generally  composed  of  a  miscellaneous  lot  of 
broken  castings  of  various  sizes  and  weights  and  of  varying  degrees  of 
roughness  and  irregularity.  The  rattler,  with  its  charge  of  brick  and 
shot,  was  then  rotated  for  some  time,  and  the  loss  in  weight  of  the 
brick  was  determined.  It  is  easy  to  see  that  there  was  small  chance 
of  anything  like  uniformity  in  making  this  test.  Each  individual  used 
the  rattler  which  was  available  for  the  purpose,  without  reference  to  its 
size.  The  speed  used  in  the  test  was  whatever  the  foundry  happened  to  be 
using.  The  total  number  of  revolutions  depended  also  upon  the  time 
the  rattler  was  run,  and  this  varied.  The  weight  of  the  foundry  shot 
used  and  the  size  and  condition  of  the  pieces  were  whatever  happened 
to  be  in  use  in  the  foundry  where  the  test  was  made,  though  this  was 
sometimes  varied  by  using  what  the  individual  making  the  tests  con- 
sidered to  be  better.  Some  engineers  were  somewhat  more  definite  and 
specified  that  a  given  weight  of  miscellaneous  foundry  shot  was  to  be 
used.  In  1896,  H.  J.  Burt*  reported  that  specifications  from  fifteen 
cities  showed  the  following  ranges  in  the  dimensions  of  the  rattler  and 
conditions  of  the  test:  Length  of  rattler,  24  to  54  inches;  diameter,  15 
to  40  inches;  speed,  revolutions  per  minute,  15  to  45;  duration  of  test, 
30  to  360  minutes;  weight  of  iron  in  the  charge,  50  to  800  pounds; 
Loss  permissable  in  one  hour,  3  to  10  per  cent.  These  figures  show  some- 
thing of  the  variation  in  practice  at  that  time. 

It  is  quite  evident  that  this  lack  of  uniformity  was  conducive  to  con- 
fusion. The  engineer  was  not  able  to  compare  the  brick  which  he  ac- 
cepted with  the  material  which  the  engineer  of  a  neighboring  city  re- 
jected.    The  manufacturer  could  not  tell  definitely  whether  his  product 

*The  Technograph,  University  of  Illinois,   No.   10,   p.   93. 


TALBOT]  QUALITIES   OF    HIGH    GRADE    PAVING    BRICK.  53 

would  fill  the  requirements  in  a  city  where  he  had  not  furnished  brick. 
There  was  considerable  difference  of  opinion  on  the  effectiveness  of  the 
tests  specified  in  certain  cities  in  determining  the  toughness  and  hard- 
ness of  brick.  The  amount  and  nature  of  the  foundry  shot  used  in 
some  cases  rendered  the  test  merely  an  abrasion  test.  Perhaps  the 
greatest  confusion  was  due  to  the  lack  of  explicitness  in  the  specifica- 
tions. As  an  illustration  the  following  example  is  cited.  In  1895  when 
the  writer  was  engage  by  the  city  of  Chicago  to  make  tests  of  brick 
from  thirty  yards  in  several  states  to  find  what  makes  of  brick  came 
up  to  the  requirement  of  the  specifications  that  the  loss  in  one  hour 
tesi  should  not  exceed  12  per  cent,  he  asked  for  instructions  on  the  size  of 
rattler,  speed,  and  amount  and  nature  of  the  foundry  shot  to  be  used 
in  the  test,  and  was  told  that  these  matters  had  not  been  specified 
and  that  he  was  to  use  his  own  judgment  concerning  them.  Of  course, 
in  such  cases  manufacturers  were  not  able  to  determine  what  grade  of 
brick  was  wanted,  and  municipalities  were  uncertain  about  the  quality 
of  the  pavement  which  they  were  putting  down. 

A  number  of  efforts  were  made  to  standardize  the  rattler  test.  One 
of  the  earliest  attempts  was  made  by  Prof.  Ira  0.  Baker,  in  1890,  by 
subjecting  brick  which  had  seen  service  in  a  pavement  and  pieces  of 
natural  stones  cut  to  standard  form  and  size  to  the  action  of  a  rattler 
in  which  were  also  placed  small  pieces  of  scrap  iron.  This  method  was 
unsatisfactory  on  account  of  the  trouble  and  expense  of  preparing  the 
test  pieces  of  natural  stone  and  the  lack  of  uniformity  in  the  stone,  as 
well  as  because  as  used  it  did  not  properly  combine  the  two  actions  of 
impact  and  abrasion.  Later,  the  same  investigator  made  a  series  of  tests 
using  2-inch  cubes  of  brick  and  stone  with  a  charge  of  foundry  "stars," 
but  this  method  did  not  prove  satisfactory. 

In  1895  the  National  Brick  Manufacturers  Association  appointed 
a  commission  to  investigate  the  subject  of  paving  brick  tests  and  to 
recommend  standard  methods  for  their  conduct.  This  commission  was 
made  up  of  representative  men,  and  they  had  unusual  facilities  for  their 
investigation.  The  work  done  marked  a  distinct  advance  in  the  testing 
of  paving  brick.  The  report  of  this  commission*  made  in  February, 
1897,  contains  much  valuable  data  on  the  subject  of  testing  paving  brick. 
The  investigation  of  the  rattler  test  was  made  by  Prof.  Edward  Orton, 
Jr.,  of  Ohio  State  University.  His  experiments  were  conducted  upon 
Canton  red  granite  repressed  brick  pavers,  burned  so  as  to  have  a  high 
degree  of  uniformity.  These  brick  were  of  as  high  quality  as  is  gen- 
erally available  for  paving  purposes.  A  general  summary  of  the  results 
of  Professor  Orton's  investigation  of  the  rattler  test  may  prove  of 
interest  in  this  discussion. 

Tests  were  made  with  charges  of  foundry  shot  made  up  of  small 
scraps  which  had  been  used  in  a  foundry  as  an  abrasive  to  clean  rough 
castings.  These  pieces  composing  the  foundry  shot  were  small,  aver- 
aging less  than  one-half  pound  and  in  no  case  being  more  than  one  and 
one-half  pounds.     The  resulting  loss  was  small  and.  of  course,  was  due 


'Pamphlet  published  by  T.  A.  Randall  &  Co.,  Indianapolis,  Ind. 


54  PAVING    BRICK    AND    PAVING   BRICK   CLAYS.  [bull.  no.  9 

almost  wholly  to  abrasive  action,  the  impact  effect  being  very  slight. 
Cast-iron  bricks  weighing  approximately  seven  pounds  each  were  next 
used  in  the  rattler.  Charges  of  these  cast-iron  shot  equivalent  to  10,  15, 
20  and  25  per  cent  of  the  volume  of  the  rattler  were  tried,  five  paving 
brick. being  tested  each  time.  The  bricks  subjected  to  this  test  sustained 
comparatively  little  loss  by  abrasion,  the  principal  loss  being  by  break- 
ing and  chipping.  The  effect  of  the  impact  with  these  heavy  shot  was 
very  severe.  Without  trying  another  size  of  shot  or  attempting  to 
blend  the  abrasive  and  impact  effect  by  means  of  a  mixture  of  sizes,  the 
use  of  iron  was  abandoned,  though  Professor  Orton  felt  that  its  cheap- 
ness, its  long  life,  and  its  uniformity  at  all  parts  of  the  country  would 
make  it  particularly  suited  for  a  standard  filling  if  its  action  as  an 
abrasive  were  favorable. 

Tests  were  then  made  using  natural  stone  of  the  general  size  of  pav- 
ing brick.  It  was  found  that  limestone,  sandstone,  and  granite  were 
as  variable  in  their  losses  as  are  brick,  that  the  results  obtained  with 
the  paving  brick  when  tested  with  blocks  of  stone  were  exceedingly 
erratic,  and  that  the  accompanying  expense  and  trouble  themselves 
rendered  this  method  unacceptable. 

Tests  were  made  with  paving  brick  alone  in  the  rattler,  no  other 
abrasive  or  filling  material  being  used.  After  an  elaborate  set  of  tests 
made  with  a  few  of  determining  the  best  speed,  size  of  charge,  etc.,  Pro- 
fessor Orton  reported  that  with  brick  alone  in  a  rattler  of  28-in.  diameter 
the  volume  of  the  charge  of  brick  should  be  from  10  to  15%  of  the  vol- 
ume of  the  rattler,  the  test  should  be  continued  for  at  least  1500  revolu- 
tions, that  the  speed  should  be  between  24  and  36  revolutions  per  min- 
ute, and  that  the  length  of  the  rattling  chamber  should  not  be  less  than 
18  inches.  These  conditions  were  found  to  give  the  least  variation  in 
results,  the  most  severe  wear,  and  to  be  the  most  convenient. 

The  commission  also  had  the  advantage  of  the  tests  made  by  Mr. 
E.  F.  Harrington,  of  the  testing  department  of  the  city  of  St.  Louis, 
which  were  along  the  same  lines  and  gave  confirmatory  evidence.  Pro- 
fessor Orton's  report  submitted  specifications  for  the  conducting  of  a 
standard  rattler  test  and  these  were  adopted  by  the  commission  almost 
without  modification.  These  specifications  are  now  known  as  the  old 
National  Brick  Manufacturers  Association  test  and  sometimes  as  Orion's 
test.  The  making  of  a  standard  for  the  size  and  speed  of  rattler  and 
for  the  charge  was  a  great  step  in  advance,  but  the  peculiar  feature  of 
the  test,  the  use  of  brick  alone  in  the  rattler,  did  not  prove  to  be  a 
fortunate  arrangement,  as  it  was  soon  shown  that  this  test  failed  to 
discriminate  to  a  sufficient  degree  between  good  and  poor  paving  brick. 
This  feature  has  since  been  eliminated,  and  a  definite  charge  of  cast- 
iron  shot  is  now  used  in  the  standard  test.  However,  as  its  reproduction 
here  may  make  it  convenient  for  reference  for  some,  the  specifications 
adopted  by  the  Paving  Brick  Commission  of  the  National  Brick  Man- 
ufacturers Association  are  here  given. 


talbot]  QUALITIES    OF    HIGH    GRADE    PAVING    BRICK.  00 

ORIGINAL    SPECIFICATIONS    FOR    A    STANDARD    METHOD    OF    CON- 
DUCTING THE  RATTLER  TEST  FOR  PAVING  BRICK.      (KNOWN   AS 
THE  OLD  N.  B.  M.  A.  TEST  OR  ORTON'S  TEST). 

I.     Dimensions  of  the  Machine. 

The  standard  machine  shall  be  28  inches  in  diameter  and  20  inches  in 
length,  measured  inside  the  rattling  chamber. 

Other  machines  may  be  used  varying  in  diameter  between  26  and  30  inches, 
and  in  length  from  18  to  24  inches,  but  if  this  is  done  a  record  of  it  must  be 
attached  to  official  report.  Long  rattlers  may  be  cut  up  into  sections  of  suit- 
able length  by  the  insertion  of  an  iron  diaphgram  at  the  proper  point. 

II.  Construction  of  the  Machine. 
The  barrel  shall  be  supported  on  trunnions  at  either  end;  in  no  case  shall 
a  shaft  pass  through  the  rattling  chamber.  The  cross  section  of  the  barrel 
shall  be  a  regular  polygon,  having  fourteen  sides.  The  heads  and  staves 
shall  be  composed  of  gray  cast  iron,  not  chilled  or  case  hardened.  There 
shall  be  a  space  of  one-fourth  of  an  inch  between  the  staves  for  the  escape 
of  dust  and  small  pieces  of  waste.  Other  machines  may  be  used  having 
from  twelve  to  sixteen  staves,  with  openings  from  one-eighth  to  three-eighths 
of  an  inch  between  staves,  but  if  this  is  done  a  record  of  it  must  be  attached 
to  the  official  report  of  the  test. 

•III.     Composition  of  the  Charge. 
All  tests  must  be  executed  on  charges  composed  of  one  kind  of  material  at 
a  time.     No  test  shall   be   considered   official   where   two   or  more   different 
bricks  or  materials  have  been  used  to  compose  a  charge. 

IV.     Quantity  of  the   Charge. 
The  quantity  of  the   charge   shall   be   estimated   by   its  bulk   and   not   its 
weight.    The  bulk  of  the  standard  charge  shall  be  equal  to  15  per  cent  of  the 
cubic  contents  of  the  rattling  chamber,  and  the  number  of  whole  brick  whose 
united  volume  comes  nearest  to  this  amount  shall  constitute  a  charge. 

V.  Revolutions  of  the  Charge. 

The  number  of  revolutions  for  a  standard  test  shall  be  1,800  and  the  speed 
of  rotation  shall  be  30  per  minute.  The  belt  power  shall  be  sufficient  to 
rotate  the  rattler  at  the  same  speed,  whether  charged  or  empty.  Other  speeds 
of  rotation  between  24  and  36  revolutions  per  minute  may  be  used,  but  if 
this  is  done  a  record  of  it  must  be  attached  to  the  official  report. 

VI.  Condition  of  the  Charge. 

The  bricks  composing  a  charge  shall  be  dry  and  clean,  and  as  nearly  as 
possible  in  the  condition  in  which  they  are  drawn  from  the  kiln. 

VII.     The  Calculation  of  the  Results. 
The  loss  shall  be  calculated  in  per  cents  of  the  weight  of  the  dry  brick  com- 
posing the  charge,  and  no  result  shall  be  considered  as  official  unless  it  is 
the  average  of  two  distinct  and  complete  tests,  made  on  separate  charges  of 
brick. 

The  abandonment  of  cast-iron  shot  as  a  feature  of  the  rattler  test 
was  not  in  accord  with  the  experience  of  others,  and  many  engineers 
felt  that  it  was  a  mistake.  The  results  of  tests  made  independently  of 
the  Paving  Brick  Commission  pointed  to  this  conclusion.  The  use  of 
high  grade  brick  only  in  the  X.  B.  M.  A.  investigation  of  this  new 
form  of  test  was  itself  an  element  of  weakness  and  a  very  bad  feature 
as  it  proved  to  be. 

Among  experiments  which  threw  some  light  on  the  discussion  which 
came  up  about  the  efficacy  of  the  new  test  were  those  conducted  at  the 


56  PAVING   BRICK   AND    PAVING   BRICK   CLAYS.  [bull.  no.  9 

University  of  Illinois  from  1895  to  1899  under  the  direction  of  the 
writer  to  determine  the  best  composition  of  the  rattling  material.  The 
investigation  showed  that  shot  composed  of  small  pieces  gave  an  effect 
which  was  almost  wholly  abrasive  and  that  the  heavier  cast-iron  shot  pro- 
duced a  spalling  and  breaking  effect  which  was  altogether  too  severe.  It 
was  felt  that  the  rattler  test  should  include  the  effect  of  both  abrasion  and 
impact,  and  a  series  of  tests  were  made  to  determine  what  mixture  of 
two  sizes  of  shot  would  give  the  best  combined  effect  of  impact  and 
abrasion,  such  as  would  approximate  to  the  wear  of  brick  in  service  in 
the  street.  The  tests  were  conducted  principally  with  a  rattler  24-in.  in 
diameter  and  36-in.  long.  The  small  shot  were  lxiy2x2i/2-in.  with 
rounded  edges  and  weighed  about  1  pound  each.  The  large  shot  were 
2%x3%x51/4-rn.  with  edges  rounded  to  y2-in.  radius,  and  weighed 
about  8  pounds  each.  From  the  results  of  the  experiments  it  was  con- 
cluded that  for  the  24x36-in.  rattler,  150  pounds  of  8-pound  shot  and 
150  pounds  of  1-pound  shot  gave  results  with  a  satisfactory  proportion 
of  abrasion  and  impact.  When  a  rattler  18-in.  long  was  used,  one-half  of 
this  charge  was  selected.  The  speed  was  about  twenty  revolutions  per 
minute.  Twelve  brick  were  used  in  the  full  rattler  and  six  in  the  half. 
The  test  was  conducted  for  1800  revolutions.  These  tests  were  reported 
to  the  Illinois  Society  of  Engineers  and  Surveyors,  and  were  described 
in  an  article  on  standard  methods  of  tests  of  paving  brick  printed  in 
The  Technograph,*  and  reprinted  in  a  number  of  technical  journals. 
The  tests  brought  out  the  facts  that  a  combination  of  large  and  small 
shot  give  a  test  which  will  provide  both  impact  and  abrasive  effects  to 
any  degree  and  that  such  a  test  will  distinguish  soft  from  hard  brick 
to  a  fair  degree. 

The  investigations  by  the  writer  also  called  attention  to  the  fact  that 
the  test  then  adopted  by  the  National  Brick  Manufacturers  Association, 
using  brick  alone  in  the  rattler,  was  defective  in  that  it  failed  to  dis- 
tinguish in  any  marked  degree  between  hard  brick  and  soft  brick. 
Objections  were  also  made  in  various  quarters.  In  some  tests  reported 
at  that  time,  brick  called  by  the  maker  as  entirely  too  soft  for  paving 
purposes  gave  a  smaller  loss  than  the  selected  paving  brick  of  the  same 
manufacturer.  In  another  test,  three  makes  of  brick  of  the  same  gen- 
eral quality  made  practically  the  same  showing  by  other  methods  of  test- 
ing, while  by  the  National  Brick  Manufacturers  Association,  one  brick 
lost  less  than  two-thirds  of  that  lost  by  either  of  the  other  two.  It  was 
also  stated  that  in  some  instances  the  test  gave  as  good  standing  to  an 
inferior  brick  as  to  a  superior  paving  brick.  Soft  brick  soon  broke  in 
the  rattler,  and  thereafter  the  loss  was  lighter,  so  that  the  final  results 
were  likely  to  be  lower  than  would  be  expected  from  the  apparent  quality 
vof  the  brick.  In  general,  the  test  was  not  very  efficient  in  measuring 
the  toughness  of  brick.  It  seems  that  in  the  investigations  conducted  by 
Professor  Orton  the  use  of  only  one  quality  of  brick,  and  that  a  high 
grade  paver,  did  not  permit  the  real  deficiencies  of  the  test  to  be 
discovered.  The  discussion  of  this  test  created  wide-spread  interest. 
Finally,  as  a  result  of  a  paper  presented  at  the  meeting  of  the   Na- 


'The  Technograph   No.   12,   University  of  Illinois. 


talbotJ  QUALITIES   OF    HIGH    GRADE    PAVING   BRICK.  57 

tional  Brick  Manufacturers  Association  in  1899,  the  association  asked 
Professor  Or  ton  to  make  a  further  investigation  of  the  subject. 

The  report  of  this  second  investigation,  made  by  Professor  Orton,  as 
well  as  of  the  reports  of  tests  made  with  the  rattler  designed  by  Gomer 
Joins,  were  submitted  in  January,  1900,  to  a  committee  consisting  of 
Messrs.  D.  V.  Purington,  J.  L.  Hegley,  H.  A.  Wheeler,  Gomer  #Jones, 
Edward  Orton,  Jr.,  J.  B.  Johnson,  and  A.  X.  Talbot,  which  committee 
had  been  authorized  to  discuss  these  reports  for  the  National  Brick 
Manufacturers  Association.  In  the  Jones  rattler  a  few  brick  were 
clamped  edgewise  in  pockets  around  the  inside  surface  of  a  cylindrical 
rattler  and  1%-in.  cubes  of  cast-iron  were  used  for  the  impact  and 
abrading  material.  The  report  of  Professor  Orton's  tests  showed  that 
the  device  of  Mr.  Jones  embodied  several  objectionable  features  and  the 
committee  concluded  that  while  the  machine  might  appeal  to  the  public 
as  in  a  sense  representing  conditions  of  wear  in  the  street  and  while 
the  reports  show  that  the  machine  is  distinctly  more  sensitive  in  indicat- 
ing the  softer  grades  of  brick,  the  variable  amount  of  surface  exposed 
on  the  brick  and  the  discordant  results  coming  from  variations  in  sizes, 
as  well  as  other  defects  of  the  machine,  rendered  it  less  satisfactory 
as  a  general  matter  of  testing  than  the  rattler  already  in  use.  The 
series  of  tests  with  the  standard  rattler  reported  by  Professor  Orton 
enabled  a  comparison  to  be  made  between  the  National  Brick  Manu- 
facturers Association  method  in  which  brick  alone  were  placed  in  the 
rattler  and  the  method  recommended  by  the  writer  which  involved  the 
use  of  cast-iron  shot  of  two  sizes.  The  investigation  included  the  effect 
of  variation  in  quality  of  brick,  the  effect  of  a  change  in  the  amount  of 
shot,  the  effect  of  a  variation  in  the  proportion  of  small  and  large  shot, 
the  effect  of  the  speed  of  the  rattler  and  the  effect  of  size  of  the  brick 
themselves.  The  committee  in  their  report  advised  the  National  Brick 
Manufacturers  Association  to  abandon  the  old  N.  B.  M.  A.  test  and  to 
adopt  in  its  place  the  test  with  cast-iron  shot  of  two  sizes,  definite  pro- 
jDortions  of  small  and  large  shot  and  of  the  total  charge  being  adopted. 
This  report  was  presented  to  the  association  in  February,  1900,  and 
the  association  changed  its  standard  method  of  test  to  conform  with 
the  specifications  recommended  by  the  committee.  It  also  accepted  the 
recommendation  that  further  tests  and  investigations  be  made. 

The  idea  of  clamping  the  brick  in  position  seemed  a  promising  one 
and  soon  after  this  the  writer  constructed  a  rattler  in  which  the  brick 
were  securely  held  around  the  circumference  of  a  cylinder,  their  inner 
faces  thereby  forming  the  surface  d?  the  cylinder.  This  machine  will 
be  described  under  the  head  of  "Talbot-Jones  Rattler  Test."  During 
the  first  months  of  1901,  Professor  Orton  experimented  with  this 
machine  and  reported  the  results  of  the  tests  together  with  the  results 
of  tests  made  with  the  standard  rattler  to  a  committee  consisting  of 
J.  B.  Johnson,  W.  K.  Hatt,  A.  Marston,  and  A.  X.  Talbot,  in  August, 
1901.  This  committee  reported  and  recommended  a  continuance  of  the 
standard  adopted  in  1900,  on  the  grounds  that  it  is  somewhat  cheaper 
and  simpler  than  the  ordinary  rattler  in  general  use,  and  that  the  find- 
ings by  the  new  X.  B.  M.  A.  standard  tests  are  in  accord  with  the 
results  of  other  tests   and   with   the   results   of  the  use   of  the   paving 


58  PAVING    BRICK   AND    PAVING   BRICK   CLAYS.  [BULL.  no.  9 

brick  in  actual  service.  The  committee  on  Technical  Investigation  of 
the  National  Brick  Manufacturers  Association  accepted  this  report  and 
by  virtue  of  the  authority  vested  in  them  by  the  association  reaffirmed 
the  method  of  tests  adopted  in  February,  1900,  as  the  standard  rattler 
test  of  the  National  Brick  Manufacturers  Association. 

National  Brick  Manufacturers  Standard  Rattler  Test. — The  specifica- 
tions for  the  present  National  Brick  Manufacturers  Association  stand- 
ard rattler  test  thus  finally  adopted  are  here  given  in  full.  It^will  be 
seen  that  they  include  requirements  for  the  dimensions  of  the  rattler 
chamber  and  the  number  of  its  sides,  for  the  composition  of  the  charge 
in  the  number  of  the  paving  brick  or  blocks  and  the  amount  of  the  cast- 
iron  shot  and  the  sizes  and  form  of  the  shot  to  be  used,  for  the  speed 
of  the  rattler,  for  the  number  of  revolutions  for  a  test,  for  the  con- 
dition of  the  brick,  and  for  the  method  of  calculation  of  the  results. 


AMENDED  SPECIFICATIONS  FOR  THE  RATTLER  TEST. 
PRESENT  N.    B.   M.   A.   TEST. 

1.  Dimensions  of  the  Machine. — The  standard  machine  shall  be  28  inches 
in  diameter  and  20  inches  in  length,  measured  inside  the  rattling  chamber. 

Other  machines  may  be  used,  varying  in  diameter  between  26  and  30  inches, 
and  in  length  from  18  to  24  inches,  but  if  this  is  done,  a  record  of  it  must 
be  attached  to  the  official  report.  Long  rattlers  must  be  cut  up  into  sections 
of  suitable  length  by  the  insertion  of  an  iron  diaphgram  at  the  proper  point. 

2.  Construction  of  the  Machine. — The  barrel  may  be  driven  by  trunnions'  at 
one  or  both  ends,  or  by  rollers  underneath,  but  in  no  case  shall  a  shaft  pass 
through  the  rattler  chamber.  The  cross  section  of  the  barrel  shall  be  a  reg- 
ular polygon,  having  fourteen  sides.  The  heads  shall  be  composed  of  gray 
cast-iron,  not  chilled  nor  case-hardened.  The  staves  shall  preferably  be  com- 
posed of  steel  plates,  as  cast-iron  peans  and  ultimately  breaks  under  the 
wearing  action  on  the  inside.  There  shall  be  a  space  of  one-fourth  of  an 
inch  between  the  staves  for  the  escape  of  the  dust  and  small  pieces  of  waste. 

Other  machines  may  be  used  having  from  twelve  to  sixteen  staves,  with 
openings  from  one-eighth  to  three-eighths  of  an  inch  between  staves  but  if 
this  is  done  a  record  of  it  must  be  attached  to  the  official  report  of  the  test. 

3.  Composition  of  the  Charge. — All  tests  must  be  executed  on  charges 
containing  but  one  make  of  paving  material  at  a  time.  The  charge  shall 
be  composed  of  the  brick  to  be  tested  and  iron  abrasive  material.  The  brick 
charge  shall  consist  of  that  number  of  whole  bricks  or  blocks  whose  com- 
bined volume  most  nearly  amounts  to  1,000  cubic  inches,  or  8  per  cent  of  the 
content  of  the  rattling  chamber.  (Nine,  ten,  or  eleven  are  the  number  re- 
quired for  the  ordinary  sizes  on  the  market).  The  abrasive  charge  shall 
consist  of  300  pounds  of  shot  made  of  ordinary  machinery  cast-iron.  This 
shot  shall  be  of  two  sizes,  as  described  below,  and  the  shot  charge  shall  be 
composed  of  one-fourth  (75  lb.)  of  the  larger  size  and  three-fourths  (225  lb.) 
of  the  smaller  size. 

4.  Size  of  the  Shot. — The  larger  size  shall  weigh  about  seven  and  one- 
half  pounds  and  be  about  two  and  one-half  inches  square  and  four  and  one- 
half  inches  long,  with  slightly  rounded  edges.  The  smaller  size  shall  be  one 
and  one-half  inch  cubes,  weighing  about  seven-eighths  of  a  pound  each,  with 
square  corners  and  edges.  The  individual  shot  shall  be  replaced  by  new  ones 
when  they  have  lost  one-tenth  of  their  original  weight. 


TALBOT]  QUALITIES   OF    HIGH    GRADE    PAVING    BRICK.  59 

5.  Revolutions  of  the  Charge. — The  number  of  revolutions  of  the  Standard 
test  shall  be  1,800,  and  the  speed  of  rotation  shall  not  fall  below  28  nor  ex- 
ceed 30  per  minute.  The  belt  power  shall  be  sufficient  to  rotate  the  rattler 
at  the  same  speed  whether  charged  or  empty. 

6.  Condition  of  the  Charge. — The  bricks  composing  a  charge  shall  be 
thoroughly  dried  before  making  the  test. 

7.  The  Calculation  of  the  Results. — The  loss  shall  be  calculated  in  per- 
centages of  the  weight  of  the  dry  brick  composing  the  charge,  and  no  result 
shall  be  considered  as  official  unless  it  is  the  average  of  two  distinct  and  com- 
plete tests,  made  on  separate  charges  of  brick. 

Talbot-Jones  Battler  Test. — In  the  machine  constructed  by  the  writer 
in  1900  (shown  in  Plate  2)  and  named  "The  Talbot-Jones  Rattler"  by 
the  committee  of  expert  engineers,  the  head  which  forms  one  end  of 
the  rattling  cylinder  overhangs  the  frame  of  the  machine.  The  ends 
of  the  brick  are  placed  so  as  to  abut  on  this  head  and  are  securely 
clamped  by  bolts  so  that  their  inner  faces  form  the  concave  surface  of  the 
rattler  cylinder.  Spacers  of  wood  of  triangular  or  trapezoidal  form  are 
placed  between  the  brick  to  keep  them  a  fixed  distance  apart  and  to 
aid  in  holding  the  brick  in  place.  An  end,  or  second  head  of  wood  or 
of  wire  screen,  is  bolted  on  to  close  the  cylinder.  A  sheet  of  metal  is 
fastened  to  the  head  of  the  machine  around  the  outside  of  the  circle 
of  .brick  and  holds  the  brick  in  place  during  the  process  of  inserting  them 
and  assists  in  taking  the  jar  in  making  the  test.  In  the  original  form 
this  band  was  in  a  fixed  position  and  since  brick  vary  in  thickness  it  was 
necessary  to  vary  the  spacing  in  order  to  divide  up  the  space  between 
the  bricks  throughout  the  entire  circle.  In  the  tests  made  by  Professor 
Orton  with  this  machine  the  brick  were  spaced  one  inch  or  more  apart. 
This  wide  spacing  and  the  variation  found  in  filling  the  circle  with 
bricks  of  different  thickness  seemed  undesirable.  The  machine  has  now 
been  modified  so  that  the  circle  is  adjustable  and  the  spacing  may  be 
made  uniform  throughout  the  entire  circumference.  The  average  in- 
ternal diameter  of  this  chamber  is  28  inches  and  the  machine  may  be 
adjusted  from  27y2-m.  to  28%-in.  This  permits  a  full  ring  to  be 
made  with  an  even  spacing  and  any  thickness  of  brick.  It  is  recom- 
mended that  the  space  between  brick  be  made  .^-in.  Other  details  of  the 
machine  are  that  the  end  of  the  band  lacks  about  %  incn  °^  being  in 
contact  with  the  head  of  the  machine,  this  space  being  left  for  the 
escape  of  dust  and  chips ;  the  heads  of  the  bolts  lie  in  a  T-shaped  groove 
in  the  head  of  the  machine  so  that  they  are  readily  adjustable ;  the  cen- 
tral portion  of  the  head  is  recessed  about  %  inches  so  that  the  iron  shot 
may  strike  the  brick  for  their  full  length ;  the  cover  of  the  cylinder  for 
the  same  reason  is  held  awTay  from  the  outer  ends  of  the  brick. 

It  will  be  seen  that  in  this  rattler  the  brick  themselves  form  the  outer 
surface  of  the  rattling  chamber  and  are  laid  at  right  angles  to  the 
direction  of  action  of  the  shot,  and  that  one  face  of  the  brick  receives 
the  wear  about  as  it  does  in  the  street.  The  shot  gives  the  abrading  and 
grinding  and  impact  effect.  In  many  ways  the  test  resembles  the  wear 
of  brick  in  the  street;  it  naturally  appeals  to  the  mind  as  resembling 
and  approximating  the  wear  in  the  street. 

This  method  of  testing  is  a  promising  one  in  many  directions.  The 
machine  is  a  special  one,  but  its  cost  is  hardly  more  than  the  standard 


60 


PAVING   BRICK   AND    PAVING    BRICK   CLAYS. 


[BULL.    NO.   9 


rattler.  Its  use  requires  but  little  more  skill.  The  time  taken  in 
charging  the  machine  and  in  making  the  test  is  greater,  so  that  the 
cost  of  a  test  by  the  Talbot-Jones  process  would  be  somewhat  more  than 
with  the  N.  B.  M.  A.  standard.  If,  however,  it  should  be  found  to 
define  the  wearing  qualities  of  a  brick  more  definitely  and  with  greater 
accuracy  than  does  the  ordinary  rattler,  these  features  would  not 
interfere  with  its  adoption.  While  considerable  experimental  work  has 
been  done  with  this  machine,  it  is  felt  that  the  investigation  has  not  pro- 
ceeded far  enough  to  standardize  it  nor  to  show  its  qualifications  suffi- 
ciently to  recommend  it  for  adoption  as  a  standard  for  testing  purposes. 
The  writer  has  been  unable  to  carry  on  the  necessary  investigations,  but 
he  hopes  that  full  tests  may  be  made  to  determine  its  usefulness.  All 
the  tests  which  have  been  made  are  favorable  to  its  efficiency  and  adapt- 
ability for  general  testing  purposes.  The  uniformity  of  conditions  for 
the  tests  and  the  opportunity  to  determine  relative  wear  of  individual 
brick  are  among  the  attractive  features. 

ABSORPTION    TEST. 

There  has  been  a  change  of  view  in  reference  to  the  value,  applicability. 
and  purpose  of  the  absorption  test.  In  the  early  experience  with  brick 
pavement,  soft  and  porous  brick  were  used  and  the  fear  was  expressed 
that  the  brick  would  crumble  and  disintegrate  under  the  effect  of  a  re- 

1 


5 

I'm  e 


Fig. 


f 
Day  5 

Rate  of  absorption  of  paving  brick. 


peated  freezing  and  thawing,  and  an  absorption  test  with  an  arbitrary 
limit  was  included  in  the  specifications.  This  test  was  used  without  full 
information  of  the  properties  of  the  brick  and  frequently  without  good 
judgment.  The  experience  of  years  and  tests  made  by  repeatedly  freez- 
ing and  thawing  bricks  have  established  the  fact  that  the  action  of 
freezing  and  thawing  is  not  likely  to  disintegrate  brick  of  a  high  grade 
which  will  pass  the  requirements  of  other  tests.  This  statement  should 
not  be  interpreted  to  mean  that  the  action  of  frost  and  traffic  together 
will  not  cause  disintegration  of  brick  which,  when  dry  and  cold,  would 
resist  the  wear  of  the  traffic  fairly  well.     The  improper  use  of  the  ab- 


TALBOT]  QUALITIES   OF    HIGH    GRADE    PAVING   BRICK.  61 

sorption  test  resulted  in  an  indiscriminate  condemnation  of  it  and  also 
in  a  lack  of  appreciation  of  its  value  and  usefulness  as  an  auxiliary  test 
and  as  a  means  for  studying  properties  of  the  brick.  The  absorption 
test  is  a  valuable  adjunct  for  use  in  interpreting  the  results  of  the 
rattler  and  cross  breaking  tests  and  in  studying  the  peculiarities  of 
the  particular  make  of  brick  which  will  be  put  into  a  pavement. 

A  good  paving  brick  will  absorb  water  quite  slowly,  the  rate  of 
absorption  varying  from  hour  to  hour.  Fig.  1  shows  the  rate  of 
absorption  through  the  period  of  some  days,  as  given  by  Mr.  F.  F.  Har- 
rington. If  the  outside  of  the  brick  is  more  dense  than  the  interior 
the  rate  of  absorption  is  still  slower.  A  broken  brick  or  a  rattled  brick 
will  absorb  water  more  readily  than  whole  brick  for  this  reason,  and 
such  brick  should  be  selected  for  the  test.  In  some  tests  the  brick 
have  been  partially  submerged  for  some  time  to  allow  the  escape  of  air. 
The  absorption  of  water  is  more  rapid  in  the  beginning,  is  quite  slow 
after  24  hours,  and  still  slower  after  48  hours.  The  absolute  value  of 
the  absorption  power  is  not  required,  and  for  comparative  purposes  the 
result  at  the  end  of  24  hours,  or  better,  at  the  end  of  48  hours,  will  be 
sufficient.  Brick  which  absorb  but  a  small  part  of  their  final  amount 
are  usually  so  dense  that  the  total  absorption  would  be  very  small  and  the 
variation  in  value  for  such  brick  will  not  affect  comparisons.  Since 
brick  in  their  usual  condition  contain  some  moisture,  the  sample  should 
be  dried  for  several  hours  at  a  temperature  at  or  above  the  boiling 
point  of  water.  The  method  given  below  requires  48  hours,  but  this 
protracted  period  seems  unnecessary  for  ordinary  purposes. 

The  absorption  test  should  be  conducted  under  the  following  condi- 
tions: The  test  will  be  made  on  five  brick  which  have  been  exposed 
to  the  action  of  the  rattler,  or  if  these  are  not  available,  on  five  brick 
which  have  been  broken  into  halves.  The  brick  shall  be  dried  at  a 
temperature  of  200°  to  300°  F.  for  24  hours  and  then  after  weighing 
shall  be  immersed  in  water  for  48  hours.  Before  reweighing  the  brick, 
surplus  water  shall  be  wiped  from  its  surface.  The  absorption  shall  be 
expressed  in  per  cents  of  the  dry  weight  of  the  brick. 

The  idea  that  low  absorption  is  a  guaranty  of  excellency  of  the  wear- 
ing qualities  of  paving  brick  was  held  by  engineers  for  many  years. 
As  brick  are  burned  in  the  kiln  the  amount  of  their  porosity  becomes 
less  and  less  until  a  point  is  reached  when  another  change  occurs  and 
further  burning  will  not  decrease  the  porosity.  The  absorption  test  may 
determine  or  distinguish  underburned  brick,  but  overburned  brick  may 
not  give  a  test  much  different,  from  brick  which  have  received  the  best 
degree  of  burning.  The  best  limits  for  absorption  will  vary  with  the 
clay  and  method  of  manufacture  and  will  have  to  be  determined  for  every 
make  of  brick.  This  determination  may  be  made  by  comparison  with 
the  results  of  other  tests  and  by  experience  with  the  brick.  In  other 
words,  no  general  limits  can  be  placed  for  the  absorption  test,  but 
special  limits  may  be  specified  for  particular  makes  of  bricks  used  in 
any  city.  For  a  given  brick,  then,  it  may  be  said  that  the  absorption 
test  is  able  to  distinguish  underburned  brick,  and  that  it  will  be  helpful 
in  determining  the  length  of  burning  permissible  with  a  given  grade 
and  make  of  brick. 


62  PACING   BRICK   AND    PAVING    BEICK   CLAYS.  Tbull.  no.  9 

CRUSHING    TEST. 

Tests  for  crushing  strength  are  open  to  the  objection  that  the  results 
obtained  are  extremely  variable,  especially  as  the  method  of  making  the 
test  is  not  uniform.  When  the  faces  of  the  test  cubes  are  ground  accur- 
ately to  plane  surfaces,  the  results  with  high-grade  paving  brick  are 
very  high,  running  up  to  20,000  pounds  per  square  inch.  The  use  of 
prepared  test  cubes  makes  an  expensive  and  slow  method  of  testing. 
Whole  brick  or  half  brick  are  tested  on  edge,  sometimes  with  the  bear- 
ing faces  ground  and  in  other  cases  not.  If  not  ground,  the  faces  may 
be  bedded  in  plaster  of  Paris  and  crushed  after  the  plaster  has  fully 
set,  or  the  faces  may  be  bedded  in  card-board  or  heavy  paper.  The  last 
named  method  of  testing  is  more  readily  made  and  if  at  least  five  speci- 
mens are  tested  the  average  may  be  expected  to  give  representative  re- 
sults. In  the  tests  described  in  this  paper,  half  bricks  were  tested, 
several  thicknesses  of  heavy  building  paper  being  used  as  bedding  plates. 
Soft  brick  will  give  results  as  low  as  1,000  pounds  per  square  inch,  when 
tested  by  this  method.  Occasionally  a  brick  will  run  as  high  as  18,000 
pounds  per  square  inch.  It  may  be  expected  that  overburned  or  poor 
paving  brick  will  stand  a  load  up  to  3,000  pounds  per  square  inch. 
Good  pavers  will  range  between  6,000  and  12,000  pounds  per  square 
inch. 

Crushing  strength  is  a  desirable  property  in  a  paving  brick.  The 
argument  that  such  heavy  loads  as  are  indicated  by  crushing  values  will 
not  come  upon  the  brick  and  that  the  brick  will  not  be  crushed  in  the 
street  is  a  negative  one.  There  is  a  relation  between  crushing  strength 
and  hardness.  The  stronger  the  brick  the  better  it  will  resist  wear  in 
the  pavement.  This  quality  of  strength  is  particularly  desirable  where 
pavement  is  subject  to  heavy  traffic.  In  comparing  two  bricks  giving 
about  the  same  rattler  results,  the  one  with  high  crushing  strength 
will  stand  heavy  traffic  much  better  than  the  weaker  one.  For  light 
traffic  high  crushing  strength  is  not  essential.  It  is  further  true  that 
the  crushing  test  throws  light  on  other  physical  properties  of  a  brick 
and  is  a  source  of  evidence  in  the  study  of  quality.  Generally  speak- 
ing, however,  this  test  is  not  of  a  character  to  be  included  in  specifica- 
tions, but  it  is  of  value  in  connection  with  the  study  of  the  properties 
of  different  bricks.  It  will  be  seen,  also,  that  the  cross  breaking  test 
gives  information  which  may  permit  it  to  take  the  place  of  the  crush- 
ing test. 

CROSS-BREAKING    TEST. 

The  cross-breaking  test  is  for  the  purpose  of  determining  the  general 
strength  of  the  brick;  incidentally  it  gives  evidence  of  the  toughness 
and  the  hardness  of  the  brick.  It  indicates  the  ability  to  resist  cross- 
breaking,  twisting,  or  spalling  by  concentrated  loads  and  is  an  index 
of  the  crushing  strength  of  the  brick. 

Two  objections  in  this  test  have  at  limes  been  raised;  (\)  thai  the 
quality  indicated  by  the  test  is  not  needed  in  a  paving  brick,  and  (2) 
thai  Ha'  results  of  (lie  cross-breaking  test  are  variable  and  even  erratic. 
II  is  believed,  however,  that  the  lest  is  helpful  in  judging  of  (he  quality 
and  strength  and  toughness  required  of  n  good  brick.     II  may  be  suffi- 


TALBOT] 


QUALITIES   OF    HIGH    GRADE    PAVING    BRICK. 


63 


cient  to  specify  only  a  medium  value  for  the  modulus  of  rupture,  and 
yel  a  brick  with  a  fairly  high  value  will  be  of  higher  grade.  The  brick 
which  docs  not  have  the  quality  of  high  resistance  to  cross-breaking  is 
likely  to  spall  or  break  in  the  street  and  not  to  withstand  traffic,  even 
though  the  rattler  test  may  show  a  low  loss.  Brick  which  have  the  tough- 
ness and  strength  which  go  with  a  good  modulus  of  rupture  may  show  a 
somewhat  higher  loss  by  the  rattler  and  yet  give  better  results  in  the 
street  than  other  brick  whose  rattler  losses  are  lower.  It  must  be  ex- 
pected that  there  will  be  a  variation  in  the  results  shown  in  tests  of 
individual  brick,  for  quality  varies  considerably  in  ordinary  paving 
brick.  The  rattler  tests  of  individual  brick  vary  widely.  Much  of  the 
variation  which  has  been  reported  in  the  results  of  cross-breaking  tests 
is  due  to  the  method  of  making  the  test  commonly  employed.  It  is  be- 
lieved by  the  writer  that  the  method  here  given  reduces  the  variation  due 
to  the  method  to  a  reasonable  amount  and  that  the  variation  now  found 
represents  quite  closely  the  lack  of  uniformity  in  the  brick.  With  the. 
test  made  in  the  manner  here  described  cross-breaking  tests,  if  properly 
judged,  become  a  valuable  adjunct  in  the  determination  of  the  quali- 
ties of  a  paving  brick. 

Brick  should  be  tested  as  a  beam  on  edge  with  a  span  of  6  inches  and 
with  the  load  applied  at  the  middle  of  the  span.  The  modulus  of  rup- 
ture is  determined  bv  the  usual  formula : 

s  =  iIL (i) 

2      bd2  V    ' 

where  W  is  the  load  applied,  I  is  the  span,  b  is  the  breadth  of  the  brick, 
and  d  the  depth. 

Plate  3  gives  a  view  of  a  brick  being  tested,  and  Fig.  32  shows  details. 


3ear/hq  Plates 


Pine  Block. 


I 


;< /? -*  !< —  5"- 

Fig.     2.     Arrangement    for    testing  cross-breaking  strength  of  brick. 


64  PAVING    BRICK    AND    PAVING   BRICK   CLAYS.  [bull.  no.  9 

Attention  is  called  to  the  use  of  steel  bearing  plates  and  to  the  use  of  the 
wooden  block.  The  narrow  soft  steel  plate  gives  a  bedding  on  the 
brick  which  is  slightly  adjusting  and  overcomes  the  tendency  to  cutting. 
The  knife  edges  are  slightly  curved  in  the  direction  of  their  length, 
to  allow  for  irregularities  or  warping  in  the  brick.  The  lower  knife 
edges  rest  upon  a  wooden  block  which  is  curved  laterally  somewhat  to 
allow  a  rocking  movement.  The  main  purpose  of  the  wooden  block, 
however,  is  to  allow  adjustment  by  its  compression  so  that  the  load 
will  be  more  evenly  distributed  and  so  that  the  work  of  applying  the  load 
and  making  the  test  will  extend  over  a  longer  time.  This  arrangement 
allows  a  more  accurate  determination  of  the  amount  of  the  load  and 
greater  freedom  in  making  the  test.  The  results  of  the  tests  which  are 
discussed  later  on,  show  that  this  method  gives  results  well  within  the 
range  of  uniformity  of  the  brick.  Eequirements  for  the  cross-breaking 
test  should  specify  that  the  brick  be  tested  on  edge,  that  the  span  be 
.6  inches,  that  the  knife  edges  be  slightly  curved  in  the  direction  of  their 
length,  say  with  a  radius  of  20  inches,  and  that  the  test  be  made  upon 
a  wooden  block  similar  to  the  one  shown. 

SPECIFIC    GRAVITY. 

The  test  for  specific  gravity  gives  general  information  but  is  not 
of  service  for  general  use.  The  specific  gravity  of  a  brick  depends  upon 
the  material,  the  method  of  making,  and  the  amount  of  burning.  For 
certain  clays  and  processes  the  specific  gravity  of  a  brick  depends  upon 
the  amount  of  burning,  up  to  a  certain  point,  which  varies  with  differ- 
ent clays.  A  dense,  heavy  brick  has  a  high  specific  gravity.  The  range 
of  specific  gravity  for  shale  paving  brick  is  from  2.2  to  2.4.  In  mak- 
ing tests  of  specific  gravity,  the  amount  of  water  absorbed  by  the  brick 
must  be  allowed  for.  The  brick  is  weighed  in  air  and  then  in  water 
and  again  in  air.  Then  specific  gravity  may  be  determined  by  the 
W 

formula, ,  where  W  is   the   weight  of   the    dry   brick,  W1  is  the 

W— W" 
weight  of  the  saturated  brick  in  air,  and  W"  is  the  weight  of  the  satur- 
ated brick  in  water. 

Discussion  op  Tests  and  Comparison  of  Qualities. 

A  comparison  of  the  various  tests  may  be  made  by  studying  the 
results  of  the  extensive  series  of  tests  of  brick  of  a  wide  range  of  char- 
acter and  quality  made  at  the  University  of  Illinois  for  the  Department 
of  Ceramics  and  State  Geological  Survey.  These  tests  are  more  fully 
reported  elsewhere.  The  brick  were  obtained  from  twenty-seven  man- 
ufacturers in  the  states  of  Illinois,  Ohio,  Indiana,  Missouri,  and  Kan- 
sas. From  one  to  five  grades  of  each  make  of  brick  were  obtained. 
Duplicate  rattler  tests  were  made  for  each  grade,  and  five  or  more 
brick  were  tested  in  cross-breaking  and  in  crushing  for  each  grade. 
The  bricks  used  in  the  tests  were  generally  selected  and  graded  at  the 
yards  by  a  representative  of  the  Ceramics  Department,  who  was  skilled 


talbot.]  QUALITIES   OF    HIGH    GRADE    PAVING    BBICK.  65 

in  selecting  and  grading  brick.  When  more  than  one  grade  was  ob- 
tained, the  first  selection  made  was  the  best  grade  for  paving  pur- 
poses, according  to  the  judgment  of  the  representative,  care  being 
taken  not  to  select  too  hard  burned  a  brick.  A  grade  harder  or  some- 
what overburned  and  one  softer  or  even  underburned  were  selected. 
When  there  seemed  to  be  an  opportunity  for  error  in  judgment,  inter- 
mediate grades  slightly  harder  or  softer  than  the  first  were  also  picked 
out.  The  X.  B.  M.  A.  Standard  rattler  test  was  used,  and  the  other 
tests  were  made  by  the  methods  already  described.  Eattled  brick  were 
used  in  the  absorption  tests. 

The  general  results  of  these  tests  are  plotted  in  Fig.  3.  The  three 
makes  of  brick  on  which  transverse  and  crushing  tests  were  not  made 
are  not  included  in  this  diagram.  The  average  for  the  tests  on  a  par- 
ticular grade  are  shown.  The  brick  were  placed  on  the  diagram  gen- 
erally in  the  order  of  the  rattler  loss,  the  grade  which  gave  the  lowest 
rattler  loss  being  used  to  fix  the  order  of  any  make  of  brick.  The 
crushing  strength  is  plotted  in  connection  with  the  modulus  of  rupture, 
(cross-breaking  test),  to  enable  a  ready  comparison  between  these  two 
tests  to  be  made,  the  scale  for  the  crushing  strength  being  one-third 
of  the  actual  value.  The  figures  given  with  the  modulus  of  rupture 
show  the  average  variation  of  the  modulus  of  rupture  for  the 
individual  brick  in  any  grade  from  the  mean  of  the  test  on  that  grade  as 
given  in  per  cent  of  the  mean  value  of  the  modulus  of  rupture.  In 
studying  this  diagram  attention  should  be  given  to  the  amount  of 
variation  in  the  absorption  test  for  each  make  of  brick,  to  the  range  in 
the  amount  of  absorption  producing  little  change  in  the  desirable  qual- 
ities in  some  brick  and  to  the  rapid  change  in  quality  for  small  changes 
in  absorption  for  others,  and  to  the  relation  between  the  rattler  test 
and  the  other  tests. 

Attention  is  called  to  the  following  particulars  shown  on  the  diagrams. 

Brick  No.  2. — A  range  of  absorption  from  *£%  to  3%  gives  an  excellent 
quality  of  brick,  as  shown  by  the  rattler  tests,  the  cross  bending  test,  and 
the  crushing  test.  Even  with  6%  absorption  this  brick  gives  a  good  rattler 
test  and  a  high  crushing  strength.  It  is  apparent  that  there  may  be  con- 
siderable variety  of  burning  with  this  brick  and  yet  secure  a  good  article, 
providing,  of  course,  that  the  heat  treatment  is  otherwise  suitable. 

Brick  No.  5. — In  this  make  a  change  in  the  absorption  amount  is  accom- 
panied by  a  considerable  change  in  the  quality  of  the  brick  as  shown  by  the 
rattler  test  and  the  other  tests.  Much  care  must  then  be  used  in  selecting 
the  right  degree  of  burning. 

Brick  No.  7. — This  is  a  fire  clay  brick  and  its  strength  can  not  well  be  com- 
pared with  the  other  brick.  It  seems  probable  that  the  smoothness  of  this 
material  gives  it  a  higher  rating  in  the  rattler  test  than  the  brick  should 
have. 

Brick  No.  10. — In  this  brick  the  grading  for  hardness  as  made  secured  a 
brick  with  but  a  small  range  in  the  absorption  test,  three  grades  varying  less 
than  1%  in  the  absorption  test.    All  or  these  were  of  very  good  quality. 

Brick  No.  12. — Absorption  up  to  5%  has  little  effect  upon  the  quality  of  the 
brick,  the  cross-breaking  strength  being  good  for  the  grade  having  5  per  cent 
absorption.  The  overburned  brick  is  of  poorer  quality.  The  range  in  absorp- 
tion from  one  to  five  per  cent  allows  considerable  latitude  in  the  selection  of 
the  brick. 

Brick  No.  15. — in  this  brick  the  amount  of  burning  seems  to  affect  the 
quality  very  much  and  it  is  difficult  to  say  just  what  range  of  absorption  is 

—5  G 


66 


PAVING    BRICK    AND    PAVING    BRICK   CLAYS. 


[BULL.    NO. 


allowable.  Zy2%  absorption  accompanies  a  fairly  good  brick,  but  variations 
on  either  side  of  this  are  very  detrimental  to  the  quality.  The  crushing  and 
cross  breaking  tests  for  this  brick  are  low.  All  of  these  conditions  are  indi- 
cations of  an  undesirable  brick  for  use  as  they  would  be  delivered  on  the 
street. 

Brick  No.  Ik. — This  brick  has  low  cross  breaking  and  high  absorption.  The 
samples  tested  do  not  indicate  a  first  class  brick. 

Brick  No.  16. — This  brick  permits  a  wide  range  of  burning  without  much 
change  in  its  quality. 

The  results  of  the  absorption  test  show  that  there  is  generally  little 
or  no  difference  in  the  amount  of  water  absorbed  in  overburned  brick  and 


REFERENCE  NO. 


o 


£     fe*    j.  2000 


A 


/  6.5 


ooo° 


VBoO 


O5=0 


5 


o°% 


5a     i; 


a.  .    g 


O     to 


QO 


frOQ 


Oq 


REFERENCE  NO. 


O    &5 


cLe- 


3z 


o° 


&% 


m 


TT 


OO 


JQ 


Note:. — Modulus  of  Rupture  shown  ;  r-n     C>  ushivg  Strength  shown     A 
The  values  given  for  Crushing  Strength  are  to  be  multiplied  by  3 


Fig.  3— Results  of  Tests  of  Paving  Brick. 


•TALBOT.]  QUALITIES   OF    HIGH    GRADE    PAVING    BRICK.  67 

well  burned  brick.  This  agrees,  of  course,  with  our  knowledge  of  tha 
change  which  takes  place  at  vitrification.  The  amount  of  variation  in 
absorption  between  brick  of  different  degrees  of  harness  (of  the  same 
make)  which  show  practically  the  same  good  wearing  quality  by  all  the 
other  tests  is  of  interest.  A  favorable  or  wide  range  of  absorption  for 
the  same  wearing  qualities  must  be  considered  advantageous  to  the 
manufacturer  and  also  to  the  consumer,  both  by  reason  of  the  wider 
latitude  allowed  in  burning  and  also  upon  the  ease  of  inspection  on 
the  street.  Other  brick  like  No.  10  give  a  considerable  difference  in 
appearance  with  only  a  slight  change  in  the  qualities  of  the  absorption 
test  and  without  any  marked  change  in  the  wearing  qualities  of  the 
brick.  The  absorption  test  appears  to  be  of  value  in  studying  a  given 
make  of  brick  or  in  learning  of  its  properties  and  giving  information 
bearing  upon  the  inspection  of  the  brick  delivered  on  the  street.  For 
any  given  make  of  brick  the  specific  range  of  absorption  which  will  give 
a  good  article  may  be  determined  and  required. 

The  results  show  that  generally  the  rattler  test  made  a  fair  determin- 
ation of  the  quality  of  the  brick,  if  we  may  judge  by  the  appearance 
of  the  brick,  the  results  of  other  tests,  and  the  reputation  of  the  brick. 
In  some  cases  the  rattler  test  gave  a  rank  better  than  would  be  given 
by  the  character  and  appearance  of  the  brick  and  by  the  results  of  the 
other  tests.  A  few  of  the  makes  showed  rather  high  rattler  loss  and  gave 
a  fairly  good  modulus  of  rupture  and  cross-breaking  strength  and 
uniformity,  and  some  of  these  brick  are  reported  to  have  given  excellent 
service  under  light  traffic.  Brick  17,  18,  19,  and  20  are  in  this  class. 
The  range  of  difference  between  that  of  a  single  test  and  the  mean  of 
the  duplicate  rattler  tests  averaged  from  about  .5  to  1%  for  the  better 
grades  of  brick,  although  in  one  case  the  variation  was  as  high  as  1.8% 
from  the  mean.  The  variations  are  smaller  than  is  usual  in  the  rattler 
test,  and  attest  the  care  in  selecting  the  brick.  The  value  of  the  crush- 
ing strength  was  generally  between  three  and  four  times  the  modulus 
of  rupture.  There  was  a  fairly  close  agreement  between  these  two 
tests.  A  high  value  in  one  test  was  accompanied  by  increased  values  in 
the  other  test.  Generally  speaking,  it  may  be  said  that  a  value  of  2,500 
pounds  per  square  inch  for  the  modulus  of  rupture  and  7,500  pounds  per 
square  inch  for  the  crushing  strength  may  be  expected  in  first  class 
paving  brick.  Lower  values  like  2,000  and  6,000  pounds  respectively,  are 
not  especially  objectionable.  In  the  cross-breaking  test  the  variation 
in  the  values  for  individual  bricks  is  of  interest  and  in  some  respects  this 
variation  may  be  considered  a  measure  of  the  uniformity  of  the  brick. 
As  already  stated,  the  numbers  given  with  the  cross-breaking  test  in 
Fi,H\  33  show  the  average  range  of  variation  in  the  modulus  of  rupture  for 
individual  brick  from  the  average  modulus  for  the  given  grade  expressed* 
in  per  cent  of  the  mean  modulus  of  rupture.  In  other  words,  a  range 
of  10  per  cent  means  that  if  the  difference  between  the  modulus  of  rupture 
for  each  individual  brick  and  the  average  modulus  for  that  grade  be 
expressed  in  per  cents  of  this  average  modulus,  the  average  of  the  re- 
sults for  the  given  grade  of  brick  will  be  10  per  cent.    It  will  be  noted  that 


68  PAVING    BRICK   AND    PAVING    BRICK   CLAYS.  [bull.  no.  9 

for  the  better  grades  of  brick  this  range  is  within  12  per  cent.  Attention 
is  called  to  the  much  greater  variation  in  bricks  No.  13,  15,  16  and  17. 
Since  uniformity  of  quality  in  a  lot  of  brick  is  of  considerable  import- 
ance a  test  of  this  kind  may  be  used  to  rate  different  makes  of  brick  on 
the  score  of  uniformity. 

It  should  be  understood  that  the  brick  tested  were  much  more  nearly, 
uniform  in  quality  than  would  be  obtained  in  taking  brick  at  random 
from  piles  along  the  street,  since  the  selection  was  made  with  a  view  to 
securing  uniformity.  The  variation  between  duplicate  rattler  tests  is 
therefore  smaller  than  may  be  expected  in  tests  of  brick  from  the 
street,  and  the  uniformity  in  the  modulus,  is  also  greater.  There  was 
greater  freedom  from  the  accidental  variations  which  frequently  affect 
the  rattler  test.  Although  the  rattler  test  was  fairly  discriminating  in 
determining  quality,  the  results  must  not  be  taken  to  indicate  that  the 
rattler  test  may  be  used  to  settle  the  exact  order  of  various  makes  of 
brick  with  respect  to  wearing  quality;  it  should  rather  be  considered 
a  means  of  determining  whether  a  brick  is  up  to  a  required  standard. 
The  objection  sometimes  made  that  the  rattler  test  does  not  easily  permit 
determination  of  variation  in  individual  bricks  was  not  considered  in 
the  investigation,  since  so  careful  a  selection  of  brick  was  made.  The 
information  given  in  the  cross-breaking  and  absorption  tests  is  valuable, 
and  the  usefulness  of  these  tests  is  shown,  particularly  in  connection 
with  the  study  of  the  qualities  of  different  grades  of  the  same  make  of 
brick. 

The  effect  of  size  of  the  brick  upon  the  loss  found  in  the  rattler  was 
not  included  in  these  tests.  It  is  established  that  the  brick  size  will 
sustain  a  greater  loss  than  the  block  size  of  the  same  grade  and  qual- 
ity. This  excess  is  due  to  the  greater  relative  exposure  of  the  corners 
which  chip  off  more  or  less,  and  to  the  greater  proportional  wearing 
surface  exposed  in  the  brick  size.  The  amount  of  this  difference  de- 
pends upon  various  conditions,  but  with  good  material  the  brick  size  may 
be  expected  to  lose,  say,  3  per  cent  more  than  the  block  size.  Of  course, 
only  a  part  of  this  difference  would  show  up  in  the  wear  of  pavements 
constructed  with  brick  of  the  two  sizes.  The  effect  of  accidental  differ- 
ences, or  of  variations  in  the  quality  of  the  shot,  or  of  the  smoothness 
or  other  conditions  of  the  rattler  was  not  studied,  and  will  not  be  dis- 
cussed here. 

A  study  of  Table  II  shows  that  the  best  grade  of  brick  received  in 
the  first  450  revolutions  of  the  rattler  test  from  47  to  53  per  cent  of  the 
total  loss  and  that  the  poorer  grades  lost  during  this  stage  a  smaller  per- 
centage of  their  total  loss,  as  little  as  30  per  cent  in  some  cases.  Simil- 
arly at  900  revolutions,  the  better  grades  had  received  67  to  77  per  cent 
of  their  total  loss,  while  the  poorer  grades  had  received  a  smaller  propor- 
tion of  their  total  loss.  It  seems  that  the  better  grades  wear  more  slowly, 
comparatively,  after  the  corners  are  rounded  off;  and  the  poorer  grades 
continue  to  grind  off  or  break  up  during  the  latter  part  of  the  test. 


TALBOT.]  QUALITIES   OF    HIGH    GRADE    PAVING    BRICK.  69 

This  extensive  series  of  tests  gives  data  on  a  wide  range  of  brick  and 
enables  comparison  to  be  made  of  a  wide  variety  of  conditions.  It  is  val- 
uable for  making  a  study  of  the  properties  of  paving  brick,  as  well  as 
for  making  a  comparison  of  the  various  tests  and  requirements  for  pav- 
ing brick.  It  will  be  seen  from  Fig.  3  that  the  best  grades  of  brick- 
in  the  first  ten  makes  of  brick,  as  shown  by  the  samples  tested,  are  of 
excellent  quality  and  will  make  a  durable  and  satisfactory  pavement. 
The  remaining  makes  are  less  valuable  as  paving  material,  and  be- 
sides many  of  these  may  not  be  judged  from  their  general  characteristics 
since  they  vary  widely  with  slight  changes  in  general  appearance.  The 
rattler  test  is  a  fairly  satisfactory  test  for  a  particular  make  of  brick 
in  picking  out  the  best  degree  of  burning,  etc.,  but  in  determining  the 
ranking  of  several  makes  of  brick  it  should  be  supplemented  with  the 
transverse  and  crushing  tests.  The  absorption  test  is  of  value  in  study- 
ing the  characteristics  of  a  given  make  of  brick  and  in  judging  of  the 
effect  of  changes  in  the  amount  of  burning. 

Eeference  may  well  be  made  to  the  information  which  a  careful  ob- 
server will  obtain  in  such  a  series  of  tests  by  means  of  the  ocular  exam- 
ination of  the  structure  and  appearance  of  the  brick.  It  suggests  the 
desirability  of  a  study  by  inspection  of  the  structure  and  behavior  of  the 
brick  in  connection  with  the  tests  made  on  the  brick  to  be  used. 

Kequirements  for  Paving  Brick. 

The  rigidity  of  the  requirements  to  be  inserted  in  specifications  or  to 
be  taken  as  standard  in  selecting  paving  brick  for  a  street  will  depend 
upon  the  conditions  under  which  the  brick  are  to  be  used.  The  amount 
of  traffic  and  the  methods  and  details  of  construction  used  in  the  con- 
struction of  the  pavement,  including  such  matters  as  the  kind  of  filler 
used  and  the  character  of  the  foundation,  will  naturally  have  a  bearing 
upon  the  requirements.  A  brick  may  be  used  on  a  street  where  there 
will  be  little  traffic  if  it  has  sufficient  weather-resisting  qualities  when 
it  should  be  rejected  for  use  with  heavy  traffic.  A  large  amount  of  light 
traffic  produces  less  wear  than  a  much  smaller  amount  of  heavy  traffic. 
In  a  pavement  made  with  a  high-grade  cement  filler  the  brick  will  be 
protected  and  the  effect  of  spalling  and  impact  may  be  much  less  than 
in  a  pavement  with  a  sand  filler.  In  a  similar  way  the  character  of  the 
foundation  has  to  do  with  the  grade  of  the  brick  to  be  chosen.  For  the 
purposes  of  this  article  it  will  be  sufficient  to  divide  traffic  into  four 
classes:  (1)  Very  heavy  traffic;  (2)  Heavy  traffic;  (3)  Medium  traf- 
fic; and  (4)  Light  traffic.  Very  heavy  traffic  would  be  such  as  would 
occur  in  the  business  district  of  our  large  cities  and  in  certain  districts 
of  smaller  cities.  Heavy  traffic  would  include  that  found  in  the  busi- 
ness districts  ©f  smaller  cities.  Medium  traffic  would  be  such  as  is 
found  on  the  streets  used  as  main  thoroughfares  in  the  smaller  cities. 
Light  traffic  is  such  as  is  found  in  the  remotest  residence  portions  of 
the  small  cities,  or  streets  not  frequented.  For  very  heavy  traffic  it  is  evi- 
dent that  onlv  the  very  best  brick  should  be  used   and   that  a  heavy 


70  PAVING    BRICK    AND    PAVING    BRICK   CLAYS.  bull.  no.  9 

foundation  and  .a  high-grade  filler  to  protect  the  brick  si.  mid  be  used. 
For  the  other  classes  of  traffic  the  requirements  may  be  leco  rigid  except 
that  a  high  degree  of  uniformity  in  the  brick  should  be  maintained. 

The  following  limiting  values  for  the  requirements  for  brick  for  the 
several  classes  of  traffic  are  suggested.  They  are  given  for  the  usual 
block  size  of  brick.  The  maximum  loss  by  the  N.  B.  M.  A.  standard 
rattler  test:  (1)  Very  heavy  traffic,  15  per  cent;  (2)  Heavy  traffic,  17 
per  cent;  (3)  Medium  traffic,  21  per  cent;  (4)  Light  traffic,  24  per  cent. 
For  the  brick  size,  3  or  4  per  cent  may  be  added  to  the  above  limits,  ex- 
cept that  the  brick  size  would  not  be  used  for  very  heavy  traffic.  No 
values  are  suggested  for  the  Talbot-Jones  rattler  since  the  standardiza- 
tion of  this  machine  is  not  yet  complete.  For  the  cross-breaking  test  the 
limits  for  the  modulus  of  rupture  may  be  made,  as  follows:  (1)  Very 
heavy  traffic,  3,000  pounds  per  square  inch;  (2)  Heavy  traffic,  2,500 
pounds  per  square  inch;  (3)  Medium  traffic,  2,000  pounds  per  square 
inch;  (4)  Light  traffic,  1,500  pounds  per  square  inch.  It  should  be 
noted  that  these  values  are  subject  to  modifications,  according  to  re- 
quirements of  traffic  and  conditions  of  the  brick,  and  are  not  to  be  taken 
as  iron-clad  limits.  They  are  intended  to  apply  to  average  samples  of 
brick  taken  from  piles  along  the  street.  The  requirements  for  uniform- 
ity and  the  methods  of  determining  this  uniformity  from  a  separate  con- 
sideration. The  limiting  variation  from  the  specified  value  for  the 
modulus  of  rupture  may  be  made  a  requirement.  It  is  frequently  pos- 
sible to  select  from  the  piles  of  brick  of  varying  degrees  of  quality  and 
make  tests  of  these.  In  case  that  one  of  these  grades  representing  a  cer- 
tain percentage  of  the  brick  on  a  portion  of  the  street,  say,  5  or  10  per 
cent,  falls  below  the  requirements,  they  should  be  rejected.  The  matter 
of  the  selecting  of  these  samples  will  be  discusssd  under  "Inspection." 

Inspection  of  Paving  Brick. 

In  taking  up  the  subject  of  inspection  of  paving  brick  it  must  be  ad- 
mitted that  inspection  is  generally  an  unsatisfactory  topic  to  both  con- 
tractor and  municipality.  Inspection  is  a  difficult  task  requiring  skilled 
judgment,  expert  knowledge,  intelligent  action,  and  ability  of  no  mean 
order,  as  well  as  the  qualities  of  tact,  balance  and  horse  sense.  Men 
having  these  qualities  and  available  for  this  purpose  are  rare.  It  is  not 
so  much  that  the  politician  desires  to  appoint  a  favored  citizen  or  that 
the  residents  on  a  street  feel  that  one  of  their  number  will  best  serve 
their  interests.  The  municipal  administrative  officer  will  usually  gladly 
waive  these  considerations  if  an  inspector  of  the  ideal  type  can  be  found. 
But  the  work  for  an  inspector  is  spasmodic,  and  the  season  is  short,  and 
his  importance  in  the  constructive  world  is  not  yet  so  well  established 
that  he  receives  a  high  salary;  we  must  expect  ideal  inspectors  to  be 
rare.  However,  the  first  requisite  of  paving  brick  inspection  is  a  level- 
headed and  wide-awake  inspector,  and  it  is  to  the  interest  of  all  con- 
cerned that  this  class  of  men  be  developed. 


talbot.]  QUALITIES   OF    HIGH    GRADE    PAVING    BRICK.  71 

Inspection  involves  a  study  of  the  brick  put  on  the  street.  An  in- 
spector whose  work  came  under  my  observation  selected  types  of  brick 
which  he  found — what  he  thought  to  be  soft  or  hard  or  brown  or  brittle 
or  red  or  black  or  what  not — and  made  a  lot  of  rattler  tests  and  absorp- 
tion tests  to  determine  the  relative  place  of  these  various  types  and  to  aid 
his  judgment  in  the  inspection.  This  is  a  step  in  the  right  direction.  It 
illustrates  what  was  meant  by  saying  that  tests  and  requirements  should 
be  useful  in  educating  inspector  and  citizen  and  contractor. 

.The  difficulties  of  inspection  are  increased  by  the  way  material  is 
loaded  on  cars  and  piled  on  the  streets.  Good  and  poor  are  mixed  to- 
gether indiscriminately,  even  when  the  change  of  quality  is  apparent  as 
the  wagon  is  loaded.  Lack  of  uniformity  is  the  bane  of  paving  brick. 
May  not  the  manufacturer  remedy  this  in  part  at  least,  and  place  the 
mediocre  brick  on  streets  which  want  cheap  brick  and  selected  brick 
on  streets  which  are  willing  to  pay  for  a  serviceable  article? 

Evidently  the  inspection  of  paving  brick  and  the  selection  of  the 
test  brick  form  an  important  matter,  and  upon  this  depends,  to  a  large 
extent,  the  quality  of  the  brick  used  in  the  pavement.  As  it  is  an  utter 
impossibility  to  test  any  considerable  part  of  the  brick,  great  care  must 
be  taken  to  select  representative  samples  and  samples  which  will  show 
the  variation  of  the  materials  To  make  severe  requirements  for  the 
results  of  tests  is  only  a  part  of  the  problem;  the  inspection  must  be 
efficient  and  thorough  and  wise  in  order  that  the  results  may  be  fair 
to  both  producer  and  consumer. 

It  is  obvious,  then,  that  in  addition  to  the  making  of  standard  tests 
the  work  of  supervision  of  the  pavement  must  include  a  fair  and 
definite  method  of  securing  sample  brick,  a  fair  and  general  method  for 
standards  of  rejection,  and  a  way  of  throwing  out  imperfect  brick  dur- 
ing the  time  of  laying  the  pavement  and  before  the  filler  is  applied.  The 
work  of  inspection,  then,  may  be  divided  into  the  following :  ( 1 )  A  gen- 
eral inspection;  (2)  Bough  culling  of  imperfect  and  inferior  brick  in 
pile  and  barrow;  (3)  A  culling  of  inferior  brick  as  they  are  about  to  be 
laid  and  immediately  after  they  are  laid.  In  the  general  inspection  dif- 
ferent car  loads  or  loads  of  the  same  quality  should  be  considered  to- 
gether. Samples  representing  as  near  as  may  be  the  average  of  the 
brick  of  a  given  lot  should  be  made  by  a  man  skilled  in  such  work. 
If  any  considerable  number  of  a  poorer  grade  are  to  be  found  in  any  lot, 
representative  samples  of  these  should  be  selected  and  tests  made  upon 
the  selected  brick.  If  the  results  of  the  tests  of  the  average  samples 
are  not  up  to  the  requirements  the  whole  lot  of  brick  should  be  re- 
jected. If  the  results  of  the  poorer  grade  are  also  not  up  to  the  re- 
quirements and  this  grade  constitutes  such  a  part  of  the  whole  lot  that 
they  are  not  likely  to  be  culled  carefully  during  laying,  the  lot  should 
be  rejected  with  the  provision  that  they  be  culled  and  then  reinspected. 
In  case  the  poorer  brick  in  a  pile  show  great  inferiority  by  their  ap- 
pearance it  may  be  sufficient  to  permit  workmen  to  cull  the  brick  as 
they  are  loaded  into  barrows,  but  this  arrangement  is  not  usually  very 


72  PAVING    BRICK   AND    PAVING   BRICK   CLAYS.  [bull.  no.  9 

satisfactory.  The  culling  of  brick  as  they  are  laid  in  the  street  should 
be  permitted  only  for  such  brick  as  show  by  their  size,  color,  shape,  or 
surface  defects  that  they  are  inferior  brick  and  there  should  be  few 
enough  of  this  class  to  enable  satisfactory  results  to  be  obtained.  With 
some  makes  of  brick  color  or  other  appearance  furnishes  evidence  of 
defect  or  of  inferior  grade,  but  in  other  makes  little  can  be  told  by  these 
methods  and  the  quality  can  be  established  only  by  physical  tests. 

Some  time  ago  the  writer  made  the  suggestion  that  a  desirable  solu- 
tion of  the  inspection  problem  would  be  to  have  the  brick  inspected 
at  the  yards  much  as  steel  is  inspected  at  the  mills.  This  could  be  done 
by  bureaus  of  inspection  which  would  employ  expert  inspectors,  as  is 
done  in  the  case  of  steel  inspection,  and  this  service  would  be  paid  for 
by  the  thousand  of  bricks  inspected,  or  yard  of  pavement  to  be  put  down, 
instead  of  at  a  dollar  and  a  half  a  day.  The  Bureau  of  Inspection 
would  be  given  the  requirements  specified  for  the  brick  in  the  ordinance 
and  the  contract,  and  would  certify  to  the  quality  of  the  brick.  This 
inspection  would  not  entirely  relieve  inspection  on  the  street  and  in 
the  pavement,  for  chipped,  broken,  and  otherwise  defective  brick  would 
still  show  up,  but  it  would  insure  a  better  grade  of  brick  and  would 
make  rejection  of  a  poor  lot  of  brick  less  objectionable  to  the  producer, 
and  if  properly  carried  out  would,  in  my  opinion,  result  in  great  gain 
for  both  the  manufacturer  and  the  municipality. 

Altogether,  inspection  covers  a  multitude  of  details,  involves  ever- 
lasting vigilance,  and  entails  patience  and  even  temper,  and  the  city 
which  can  get  good  inspection  is  indeed  fortunate.  A  reputation  for 
severe  inspection  is  said  to  cause  an  undue  increase  in  the  bids  for  work, 
but  this  charge  must  not  be  accepted  without  consideration.  Five  cents 
a  yard  extra  is  only  the  cost  of  a  year's  life  of  a  pavement  on  a  resi- 
dence street  or  six  months  on  a  business  street,  and  who  will  not  say 
that  the  difference  in  quality  of  brick  may  not  make  five'  or  ten  years, 
or  even  more,  difference  in  the  life  of  the  pavement?  Surely,  adequate 
and  judicious  inspection  pays  for  itself  many  times  over. 

In  this  article  the  writer  has  not  attempted  to  go  into  some  of  the 
details  of  testing  and  inspection;  he  has  discussed  principles  governing 
the  selection  of  the  brick.  Many  questions  arise  between  the  producer 
and  the  consumer,  and  these  may  not  always  be  decided  according  to 
numerical  values  of  tests.  It  seems  probable  that  brick  will  continue 
to  be  the  principal  material  for  street  pavement  in  inland  cities  of 
Illinois,  and  the  quality  of  the  pavements  may  be  improved  if  manu- 
facturers and  municipalities  agree  on  definite  and  trustworthy  require- 
ments and  tests  and  there  is  adequate  and  judicious  inspection.  An  im- 
provement in  quality  and  uniformity  will  be  advantageous  to  producer 
jind  consumer. 


TESTS  OF  PAVING  BRICKS. 

GENERAL    STATEMENT. 

The  tests  herein  reported  were  made  on  paving  brick  from  twenty- 
four  paving  brick  factories  in  Illinois,  Indiana,  Ohio,  Missouri  and 
Kansas.  The  samples  of  each  make  and  grade  were  selected  by  repre- 
sentatives of  the  State  Geological  Survey  at  the  yards  of  the  factory. 
An  effort  was  made  to  secure  representative  samples.  The  collectors 
were  familiar  with  paving  brick  and  their  properties  and  exercised  care 
in  the  selection,  and  it  is  believed  that  the  brick  obtained  are  fairly 
representative  of  the  product  of  the  various  factories  at  the  time  the 
selection  was  made.  In  many  cases  samples  of  two  to  five  grades  of 
brick,  varying  from  the  softer  grade  to  very  hard  burned,  were  ob- 
tained. The  letter  at  the  beginning  of  the  mark  or  designation  of  the 
various  samples  is  the  initial  of  the  collector  who  selected  the  brick, 
and  the  letter  at  the  end  refers  to  the  grade  of  burning  of  the  brick,  a 
being  the  softest  burned  lot.  In  some  cases  the  a  grade  was  consid- 
erably under-burned  and  in  others  it  represented  the  best  grade. 

The  brick  were  held  before  making  the  tests,  and  the  samples  which 
were  collected  early  in  the  spring  were  left  for  some  time  in  their  orig- 
inal packages  in  the  open  air  and  were  subjected  to  dampness  from  the 
spring  rains.  However,  before  the  tests  were  made,  the  brick  were 
stacked  openly  under  a  tent  and  left  for  some  time  through  hot  dry 
weather  so  that  each  brick  had  ample  opportunity  to  become  dried 
throughout.  The  bricks  which  arrived  last  came  direct  from  the  kilns 
to  the  tent  during  dry  weather  without  having  become  damp  and  were 
tested  first.  In  this  way  the  earlier  brick  were  given  from  three  to  five 
weeks  in  which  to  dry.  As  the  tent  was  open  at  the  ends  so  that  good 
circulation  of  air  prevailed,  the  bricks  had  the  opportunity  to  be  thor- 
oughly dried.  While  no  tests  were  made  on  the  amount  of  moisture  con- 
tained, it  is  thought  that  all  the  bricks  were  as  dry  as  they  could  be  under 
the  average  humidity  conditions  of  summer  weather  and  without  being 
dried  in  an  oven.  It  is  certain  that  the  amount  of  moisture  in  the 
brick  was  as  low  as  is  required  by  the  provisions  of  the  X.  B.  M.  A. 
specifications  for  the  rattler  test. 

The  rattler  test  of  the  brick  was  made  in  the  Eoacl  Laboratory  of 
the  Civil  Engineering  Department  of  the  University  of  Illinois.  The 
standard  N.  B.  M.  A.  rattler  of  the  Road  Laboratory  was  used.  The 
number  of  bricks  and  blocks  agreed  closely  with  the  standard  specifiea- 


74  PAVING    BRICK    AND    PAVING    BRICK   CLAYS.  [bull.  no.  9 

tions,  although  the  relative  cubical  content  of  the  rattler  and  the  charge 
was  not  calculated  for  each  lot,  but  the  charge  was  varied  with  the  judg- 
ment of  the  operator.  At  least  9  and  not  more  than  10  blocks  were  con- 
sidered a  charge,  and  at  least  10  and  not  more  than  12  of  the  brick 
size.  The  results  of  the  rattler  test  are  given  in  Table  I.  The  brick 
were  weighed  at  the  end  of  450,  900,  1,350  and  1,800  revolutions  and  the 
corresponding  losses  are  given  in  the  tables.  Table  II  shows  the  pro- 
portions of  the  final  or  total  loss  at  the  end  of  each  of  these  periods 
given  in  per  cent  of  the  final  loss,  and  Table  III  shows  the  percentage 
of  the  total  loss  for  each  of  the  four  stages. 

The  rattler  tests  were  made  under  the  direction  of  Mr.  E.  C.  Purdy. 
Acknowledgment  is  made  to  Professor  I.  O.  Baker  of  the  Civil  Engineer- 
ing Department  of  the  University  of  Illinois  for  the  facilities  afforded 
in  making  the  rattler  tests. 

After  the  brick  were  rattled,  five  of  each  set,  two  from  one  chamber 
and  three  from  the  other  chamber,  were  taken  to  the  Laboratory  of 
Applied  Mechanics  and  the  amount  of  absorption  determined.  The 
brick  were  not  dried  further,  but  the  conditions  were  such  that  the 
amount  of  moisture  present  would  have  little  effect  upon  the  determina- 
tions reported. 

From  the  remainder  of  the  brick  not  rattled,  as  many  as  could  be 
spared  up  to  ten  of  each  kind  were  taken  to  the  Laboratory  of  Applied 
Mechanics  of  the  University  of  Illinois,  and  the  transverse  or  cross- 
breaking  test  made  upon  them.  The  method  of  making  this  test  is  fully 
explained  in  the  paper  by  Professor  Talbot  on  the  Quality  of  a  High 
Grade  Paving  Brick  and  the  Tests  used  in  Determining  Them.  Crush- 
ing tests  were  made  on  half-brick  placed  flat-wise  as  described  in  the 
paper  just  referred  to.  The  results  for  the  absorption,  transverse,  and 
crushing  tests,  as  furnished  by  Professor  Talbot,  are  given  in  the  tables. 
The  average  values  for  absorption,  cross-breaking,  and  crushing  are  given 
in  Table  IV,  and  the  detailed  results  follow  in  Table  V.  Transverse 
and  crushing  tests  were  not  made  on  the  Purington,  Edwardsville  and 
Streator  Paving  Brick  Co.  brick. 

The  absorption  and  transverse  tests  were  made  by  Mr.  C.  H.  Pierce, 
Instructor  in  Theoretical  and  Applied  Mechanics,  and  the  crushing  tests 
by  Mr.  H.  L.  Whittemore,  Associate  in  Applied  Mechanics,  and  this 
work  was  under  the  direct  supervision  of  Professor  A.  N.  Talbot. 

The  general  selection  of  the  brick  at  the  yards  and  the  arrangements 
therefor  were  made  by  the  State  Geological  Survey.  Mr.  E.  C.  Purdy, 
of  the  Department  of  Ceramics  of  the  University  of  Illinois,  had  general 
supervision  of  the  arrangements  for  testing. 


TALBOT.] 


TESTS    OF    PAVING    BRICK. 


tO 


TABLE  I. 
N.  B.  M.  A.  Kattler  Test. 


Mark,  Name  of  Brick. 


Grade 
of  Brick. 


Average  Total 
Loss  of  Two 
Charges  at  End  of 


450    I    900      1350      1800 
Rev.   Rev.   Rev.    Rev. 


Size  of  Brick 
in  cm. 


K3b  Albion,  111 

K3c  Albion,   111 

K3d  Albion,  111 

K3e  Albion,  111 

Klb  Alton,  111 

Klc  Alton,  111 

Kid  Alton,    111 

Kle  Alton,  111 

B-IIa  Atchison,  Kan 

B-IIb  Atchison,  Kan 

Klob  Bar  Clay  Co.,  Streator.  111.... 
Kl5c  Bar  Clay  Co.,  Streator,  111.... 
Kl5d  Bar  Clay  Co.,  Streator,  111.... 
Kloe  BarClavCo.,  Streator,  111.... 

Kllb  Brazil,  Ind 

Kile  Brazil,    Ind 

Klld  Brazil,  Ind 

Kile  Brazil,   Ind 

I-IIbCaney,  Kan..   

K13b  Clinton,    Ind 

K13c  Clinton,   Ind 

Kl3d  Clinton,  Ind 

Kl3e  Clinton.  Ind 

G-lIa  Coffey ville,  Kan 

G-IIb  Coffewille,  Kan 

G-IIc  Coffeyville,  Kan 

F-Ib  Danville  Brick  Co 

F-Ic  Danville  Brick   Co 

F-Id  Danville  Brick   Co 

Fie  Danville  Brick  Co 

K5b  Edwardsville,    111 

K5c  Edwardsville,    III  

K5d   Edwardsville,  111 

K5e  Edwardsville,  111 

S2b  Kansas  City,  Mo.,    Diamond... 

L-lIb  Lawrence,  Kan 

L-IIc  Lawrence,  Kan 

K9b  Poston  B,  Crawfordsville.  Ind. 
K9c  Poston  B.  Crawfordsville,  Ind. 
K9d  Poston  B,  Crawfordsville,  Ind. 
K9e  Poston  B,  Crawfordsville,  Ind. 

J-II  Pittsburg,  Kan 

K6b  Purington  block,  Galesburg,  111 
K6c  Purington  block,  Galesburg,  111 
K6d  Purington  block,  Galesburg,  111 
K6e  Purington  block,  Galesburg,  111 
K6b2 Purington  block,  Galesburg, 111 
K6c2  Purington  block,  Galesburg,  111 

K4a  Springfield,  111 

K4b  Springfield,  111 

K4c  Springfield,  111 

K4d  Springfield,  111 

K4e  Springfield,  111 

K2a  St.  Louis,  Mo.,    hvdraulic 

K2b  St.  Louis,  Mo.,  hydraulic 

\  8c  Streator  Paving  Brick  Co 

V8d  Streator  Paving  Brick  Co 

V8e  Streator  Paving  Brick  Co 

KlObTerre  Haute.  Ind 

KlOc  Terre  Haute,  Ind 


Soft 

Alley 

No.  1  paver. 
Overburned 
Soft  burned. 

Alleys 

No.  1  paver. 
Overburned 
No.  1  paver. 

..do 

Soft 

Alley 

No.  1  paver. 
Overburned 

Soft 

Alley.. 

No  1  paver. 
Overburned 


Soft 

Alley 

No.  1  paver.. 
Overburned 
Brick 


No.  1  block. 

Soft 

Alley 

No.  1  paver. 
Overburned 

Soft 

Alley 

No.  1  paver 
Overburned 
No.  1  paver . 

.  .do 

No.  2  paver. 

Soft 

Alley 

No.  1  paver 
Overburned 
No.  1  paver. 

Soft 

Alley 

F3o.  1  paver. 
Overburned 


No.  1  paver. . 

Soft 

Alley 

No.  1  paver. . 
Over-burned 
No.  1  paver. . 


Soft 

Alley 

No.  1  paver. 

Soft 

Alley 


18.5 
11.3 
12.7 
11.1 
17.4 
13.3 
8.4 
9.4 


13.6 
14.5 
10.2 
10.3 

9.1 
28.9 
13.6 
13.5 
14.5 

9.7 
161 
14.5 
12.9 
14.4 


5  6 


19.3 

12.7 

9.1 

9.8 

17.8 

12.6 

7.3 

8.2 

14.8 

10  4 

8.7 

14.3 

8.9 

6.4 

6.1 

8  4 

7.8 

7.5 

5.8 

8.4 

HI 


29.5 
17.5 
19.0 
18.6 
28.6 
21.5 
11.5 
16.2 


19.5 
20.9 
15.4 
13.9 
14.5 
45.1 
20.1 
20.1 
23.5 
17.3| 
26.0 
22.7 
19.6 
21  6 


8.5 


19.7 
9.2 
9.9 

14.8 


7  9 
14.7 
10.7 
10.6 
23.1 
19.9 


29.3 
19.8 
13.9 
17.2 
28.7 
19.5 
12.5 
12.2 
20.9 
15.2 
11.0 
23.6 
14.3 
9.7 
9.3 
12.3 
13.4 
11.7 
9  1 
12.9 
23.7 
16.6 


30.6 
14.5 
14.2 
18.9 


12.2 
20.1 
16.8 
15.5 
32.8 
28.2 


21.2 

22.5 
24.1 
40.0 
28.2 
14.1 
21.8 


23.9 
25.4 
19.0 
16.7 
18.7 
56.8 
25.3 
24.5 
30.8 
22.0 
33.6 
29.0 
26.2 
27.5 


10.9 


38.9 
25.1 
17.6 
23.3 
37.0 
24.3 
16.3 
15.2 
24.9 
18.8 
16.0 
31.9 
18.0 
12  4 
11.8 
15.1 
18.2 
15.4 
11.6 
16.5 
31.7 
21.9 


38.2 
17.0 
16.9 


14.2 
25  2 
21.6 
18.4 
40.8 
32.9 


46.2 
24  6 
24.9 
26.4 
46.1 
33.9 
15.8 
27.0 
28.0 
27.9 
29.5 
21.8 
18.4 
22.0 
67.1 
29.8 
28.1 
36.7 
25.7 
41.6 
34.7 
31.5 
31.6 
13.7 
12.8 
15.0 
46.7 
30.2 
20.8 
28.4 
44.9 
28.7 
19.4 
18.1 
27.9 
22.9 
18.6 
39.5 
21.7 
14. 81 
13.7 
17.1 
22  8 
18.3 
13.3 
20.3 
38.6 
26.6 
19.8 
45.2 
19.9 
19.1 


17.5 
15.9 
29  0 
21.3 
21.9 
46.5 
35.7 


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20.5x9.5x6.5 


20x9.5x6.5 

23x10x9 

23x10x9 

22  5x10x9 

22.5x9.5x9 

20.5x9.75x6.5 

21.5x10.2x8.9 

21.5x10  2x8.9 

20.9x10.2x8.9 

20.9x10.2x8.9 

21.5x10.2x8.9 

21.5x10.2x9.5 


22x10.5x7 

21x9  5x6.7 

21x10x6.5 

21x10x6.5 

21x10x7 


20.9x10.2x5.7 

20.3x10.2x5.7 

20.3x10  2x5  7 

22x10x8.5 

21.5x10x8 


76 


PAVING   BRICK   AND    PAVING   BRICK   CLAYS.  [bull.  no.  9 

TABLE  I- Concluded. 


Mark,  Name  of  Brick. 

Grade 
of  Brick. 

Average  Total  # 

Loss  of  Two 

Charges  at  End  of 

Size  of  Brick 

450 
Rev. 

900 
Rev. 

1350 
Kev. 

1800 
Rev. 

in  cm. 

KlOd  Terre  Haute,  Ind        

No.  1 
( >ver- 

paver 

-burned 

22.6 
19.0 

29.8 
26.7 

35.3 

32.0 

39.4 

36.1 
33.0 
29.6 

53.5 

28.1 

20.2 

21  5x10x8 

KlOe  Terre  Haute,  Ind 

22x10x8  5 

H  - 1 J  a  Topeka,  Kan 

21x9.5x6.5 

H-I I b  Topeka,  Kan 

14.1 

26.5 

11.3 

10.2 

12.5 
8.4 

20.5 

32.7 

17.6 

15.0 

18.7 
13.4 

26.6 
45.6 
24.2 

18.5 

K8b  Wabash  Clay  Co.,  Veedersburg 
Indiana 

Soft  . 

Alley 

No.  1 

Over- 
No.  1 
.  .do . . 

No.  1 
.  .do . . 

23.5x10x9 

K8c  Wabash  Clay  Co.,  Veedersburg, 

23  5x10x9 

K8d  Wabash  Clay  Co.,  Veedersburg 
Indiana 

paver 

-burned  

paver 

22.5x9.75x8.5 

K8e  Wabash  Clay  Co.,  Veedersburg 

23x10x9 

K14b  Western  Brick  Co., Danville.lll 
K14a  Western  Brick  Co.,Danville,Ill 

17.3 

20.8 
21.2 

23x10x8.5 

R3a  Imperial,  Canton,  O     

600 
Rev. 

12C0 
Rev. 

1800 
Rev. 

14.2 
14.8 
26.3 
16.9 
18.2 
17.8 
18.6 
15.3 
16.7 

22x10x9 

8.7 
13.9 

12.2 
20.9 

Sib  Moberlv,   Mo 

20x9x8.5 

No.  1 
.  .do . . 

23  3x10x8  2 

Rib  Nelson ville,  O 

9.0 

13.9 

R2a  Portsmouth.  O 

.  .do . . . 

22.75x9.9x8 

R2b  Portsmouth,  O  . 

..do  . 

9.8 

14.8 

R4a  Royal,    Canton,  O 

.do . . 
..do  . 

21.8x10x9 

R4b  Royal,    Canton,  O 

10.3 

10.7 

TALBOT.] 


TESTS    OF    PAVING    BRICK. 


77 


TABLE  II. 
Proportional  Rattler  Loss. 


450  Rev. 

900  Rev. 

1350    Rev. 

1800    Rev. 

K8b 

40.1 

46  0 
51.0 
41.9 
37.7 
39.2 
53.3 
34.9 
48.8 
49.2 
47.0 
56.1 
41.2 
43.1 
45.7 
48.0 
39.5 
37.1 
38.8 
41.7 
40.8 
45.6 
44.0 
41.4 
42.1 
43.8 
34.4 
52.9 
45.4 
46.9 
36.0 
42.0 
43.3 
44.3 
49.2 

63.9 
70.9 
76.4 
70.3 
62.0 
63.3 
72.7 
59.8 
69.7 
70.9 
71.8 
75.5 
66.0 
67  2 
67.5 
71.4 
64.2 
67.4 
62.2 
65.3 
62.1 
68.4 
66.6 
62.8 
65.7 
66.6 
60.7 
74.7 
66.5 
58.9 
59.7 
67.4 
65.4 
67.7 
71.5 

63.0 
86.3 
90.4 
87.5 
82.4 
83.2 
89.0 
80.7 
85.5 
8v 3 
87.2 
90.7 
84.9 
84.6 
84.8 
87.0 
84.0 
85.6 
80.6 
83.4 
83.2 
87.3 
85.3 
83.3 
83.2 
84.6 
82.2 
89.1 
82.0 
85.9 
80.8 
85.0 
83.4 
85.5 
88.1 

100  00 

K3c 

100  00 

K3d 

100  00 

K3e....                                 ..   . 

100  (.0 

Klb 

100.00 

Klc* 

100  CO 

Kid 

100.00 

Kle 

Bllb 

100.00 
100.00 

Klob 

Kl5c ..     . 

103.00 
100  00 

Kl5d 

100  00 

Kloe 

100.00 

Kllb 

300.00 

Kile 

103. CO 

KUd 

Kile 

100  00 
100. CO 

Illb 

100  00 

Kl3b 

100. CO 

Kl3c 

100.00 

Kl3d 

1C0. 00 

Kl3e 

100.00 

Glib 

100.00 

Fib 

100.00 

Flc ;... 

100.00 

Fid 

100  00 

1C0. CO 

S2b 

100.00 

Lllb 

100. CO 

Lllc 

100.00 
100  00 

K9c  

1C0. 00 

100.00 

K9e 

100.00 

Jllb 

100.00 

K4a  

K4b 

K4c  

43.7 
46.2 
51.8 

67.8 
72.6 
74.2 

84.6 
85.3 
88.3 

100.00 

100. CO 

K4d 

100  00 

K4e 

K2b 

50.0 
49.6 
55.6 
57.3 
52  7 
47.7 
49.5 
40.3 
50.3 
40.2 

76.8 
70.4 
78.9 
75.7 
74.1 
69.3 
61.1 
62.7 
74.1 
64.2 

89.8 
87.7 
92.1 
89.6 
88.9 
87.8 
85.2 
86.2 
91.2 
83.2 

100.00 

100.00 

KlOc  

100. CO 

KlOd 

100. CO 

KlOe 

100.00 

100. CO 

K8b 

100.00 

K8c  

100. CO 

K8d 

100.00 

Kl4b 

100  00 

R3b  

600  Rev. 
59.0 
53.1 
49.5 
52.4 
61.6 

1200    Rev. 
82.6 
79.4 
76.6 
79.4 
82.2 

1800  Rev. 
100.(0 

100.00 

Rib  

100.00 

100. CO 

R4b  

100.00 

78 


PAVING    BRICK    AND    PAVING    BRICK   CLAYS. 


[BULL.    NO.   9 


TABLE  III. 
Showing  Percentage  of  the  Total  Loss  in  Each  Stage  of  Rattler  Loss. 


0-450 
Rev. 

450-900 
Rev. 

900-1S50 
Rev. 

1350-1800 
Rev. 

K3b 

40.2 
46.1 
51.0 
41.9 
37.7 
39.2 
53.3 
48.8 
49.2 
47.0 
56.1 
41.2 
43.1 
45.7 
47.9 
39.5 
38.0 
38.8 
41.7 
40.8 
45.6 
44.0 
41.4 
42.1 
43.8 
34.4 
52.9 
45.4 
46.9 
36.0 
42.0 
43.3 
44.3 
49.2 
43.6 
46.2 
51.4 
50.0 
49.6 
55.7 
57.3 
52.8 
47.7 
49.5 
40.3 
50.3 
40.2 

23.8 
24.8 
25.4 
28.4 
24.3 
24.1 
19.4 
20.9 
21.7 
23.8 
19.5 
24.8 
24.1 
21.8 
23.4 
24.7 
29.4 
23.5 
23.6 
2J.3 
23.8 
22.6 
21.4 
23.6 
22.8 
26.3 
21.8 
21.1 
12.1 
23.7 
25.4 
22.2 
23.4 
22.3 
24.2 
26.3 
22.4 
26.8 
20.8 
23.3 
18.4 
21.5 
21.5 
11.6 
22.4 
23.8 
24  1 

19.1 
15.4 
14.9 
17.2 
20.4 
19.9 
16.3 
15.8 
15.4 
16.5 
15.1 
18.8 
17.4 
17.3 
15.7 
19.8 
18.3 
18.4 
18.1 
21.1 
18.9 
18.7 
20.5 
17.5 
18.0 
21.6 
14.4 
15.5 
27.0 
21.1 
17.6 
18.0 
17.8 
16.7 
16.8 
12.7 
14.0 
13.0 
17.3 
13.2 
13.9 
14  7 
18.5 
24  2 
22.5 
17.2 
19.0 

17  0 

K3c 

13.7 
9.7 
12  5 

K3d 

K3e 

Klb 

17  6 

Klc 

16  8 

Kid 

11  0 

Bllb 

14  5 

Kl5b 

18  7 

K15c 

12  8 

Kl5d 

9  3 

Kloe.. 

15  1 

Kllb 

15  4 

Kile. 

15  2 

Klld 

12  9 

Kile 

16  0 

Illb 

14  4 

Kl3b 

19  4 

16  6 

Kl3d 

16  8 

12  7 

Glib 

14  7 

Fib 

16  7 

Flc 

16  8 

15  4 

Fie 

17  7 

10  9 

Lllb 

18  0 

14  1 

K9b 

19  2 

K9c 

15  0 

K9d 

16  6 

K9e 

14  5 

Jllb 

11  9 

15  4 

K4c 

14  8 

11  7 

K2b 

10  2 

KlOb 

12.3 

KlOc 

7  9 

10  4 

KlOe.  . 

11  1 

12  2 

K8d 

14  8 

K8c 

13  8 

K8b 

3.8 

K14b 

16.8 

0-600 

Rev. 
59.1 
54.1 
49.5 
52.4 
61.6 

600-1200 
Rev. 
23.5 
26.3 
27.1 
27.0 
20.7 

1200,1800 
Rev. 
17  4 

Sib 

20  6 

23  4 

R2b 

20  6 

17  8 

TALBOT.] 


TESTS    OF    PAYING    BRICK. 


79 


TABLE  IV* 
Abstract  of  Report  of  Tests  of  Paving  Brick. 


Name  of  Brick. 

Lab.  No. 

Per  Cent 

Abs. 
Water. 

Modu- 
lus of 
Rupture. 

Ciush- 

ing 
Strength 

K3b 
K3c 
K3d 
K3e 

Klb 
Klc 
Kid 
Kle 

B2 

Kl5b 
K15c 
Kl5d 
K15e 

12 

H2 

K13b 
K13c 
Kl3d 
K13e 

10.0 
3.5 
1.05 
0.7 

11.2 
6.1 
0.9 
1.2 

995 
2100 
2350 
2700 

"Alton,"  Alton,  111.                       

4500 
48C0 
3200 

1630 
2535 
1420 

1S00 

1776 

2365 
2600' 
2870 

1970 

2300 

1240 

1280 
1620 
1500 

4000 
8400 

Atchison,  Kans 

"Barr  Clay  Co.,"  Streator,  111 

7.67 
1.0 
0.83 
0.8 

3.416 

1.27 

9.3 
6.9 
1.7 
1.1 

7800 

"Caney  Brick  Co  , "  Caney,  Kans    . 

11200 
11700 
8500 

"Clinton,"  Clinton,  Ind 

2700 

"The  Coffeyville  Brick  and  Tile  Co" 

6000 
5600 

"Coffey ville  Brick" 

G2 
G2 

Fib 
Flc 
Fid 
Fie 

S2b 

K2a 
K2b 

Kllb 
Kile 
Klld 
Kile 

L2b 
L2c 

R4a 

R4b 

R3a 
R3b 

Sib 

Rla 

Rib 

R2a 

R2b 

J2 

K9b 
K9c 
K9d 
K9e 

0.8 
0.83 

13.2 
4.8 
2.8 
1.7 
0.72 

2320 
1900 

6500 

"Coffeyville  Block" 

"Diamond,"  Kansas  City,  Mo 

1700 

980 

1670 

2410 

5200 
3400 
6100 

'TI  ydrulic, ' '  St.  Louis,  Mo 

0.6 

13.1 
2.9 

1.89 
2.7 

8.6 
0.94 

2430 

685 
1510 
2260 

870 

1770 
1960 

8300 

Lawrence ,  Kans , 

"Metropolitan  Block,"  Canton,  Ohio.. 

10000 

"Metropolitan  Block"  (Imperial),  Canton,  O 

1.05 

3130 

7600 

"Missouri, "  Moberly,  Mo 

1.27 
3.313 

2800 
2130 

7200 

"Nelsonville,"  Nelsonville,  Ohio 

"Peebles  Block,"  Portsmouth,  Ohio 

1.68 

1790 

38C0 

2.211 

2.313 

10.2 
6.3 
2.513 
0  8 

2505 
2220 

705 

10S0 
2050 
2050 

Pittsburg,  Kans 

"Poston  Block,"  Crawfordsville,  Ind 

3900 

8400 
9800 
10300 

80 


PAVING    BRICK    AND    PAVING    BRICK   CLAYS.  [bull.  NO.  9 

TABLE  IV '-Concluded 
Abstract  of  Report  of  Tests  of  Paving  Brick. 


Name  of  Brick. 

Lab.  No. 

Per  Cent 

Abs. 

Water. 

Modu- 
lus of 
Rupture 

Crushi'g 
Strength 

Springfield,  111 

K4a 
K4b 
K4c 
K4d 
K4e 

KlOb 
KlOc 
KlOd 
KlOe 

K8b 
K8c 
K8d 
K8e 

K14a 
Kl4b 

12.2 
5.0 
1.16 
0.6 

9.1 
2.0 
1.03 

0.8 

9.9 
3.9 
3.9 
1.6 

980 
2360 
2250 
1890 

1375 
1910 
2340 
1880 

585 
1035 
1440 

810 

2100 
52CO 

"Terre  Haute  Block,"  Terre  Haute,  Ind 

3603 

"Wabash  Clay  Co.,1'  Culver  Block,   Veedersburg,  Ind 
"Western  Paver,"  Danville,  111 

6000 
2400 

2700 
44CO 
7600 
4400 

4.218 

1617 

5200 

TALBOT] 


TESTS   OF    PAVING    BRICK. 


81 


TABLE  V. 


K3b-ALBION,  ILL. 
Transverse. 


No. 

Breadth- 
inches. 

Depth- 
inches. 

Span- 
inches. 

Load- 
pounds. 

Modulus 

of 
Rupture- 
pounds 
per  sq    in. 

Av.Mod. 

Variation 

from 
average. 

Per  cent 
variation. 

1 

3.25 
3.30 
3.28 
3.22 
3.28 
3.25 
3.20 
3.22 
3.30 

4.25 
4.25 
4.28 
4.15 
4.40 
4.25 
4.15 
4.08 
4.25 

6 

6 
6 
6 
6 
6 
6 
6 
6 

Av 

6020 
6560 
5500 

6260 
6770 
6030 
7180 
8160 
4550 

925 
990 
820 
1020 
1050 
925 
1170 
1370 
690 

995 

—  70 

—  5 
-175 

+  25 
+  55 

—  70 
+175 
+375 
-305 

7.0 
0.5 

3 

17.6 

4 

2.5 

.-) 

5.5 

ti 

7.0 

17.6 

8 

9  . 

37.7 
30.6 

57030 

8960 

126.0 

6337 

995 

14.0 

Absorption. 


Kilos. 

Number. 

Dry. 

Wet. 

Gain. 

Per  cent. 

b.l 

2.385 

2.72 

2.65 

2.04 

2.23 

2.615 
2  965 
2.885 
2.285 
2.46 

.23 

.245 

.235 

.245 

.23 

Average  .... 

9.7 

2.::::::::::::.-::.:..:::::.::.::::: 

9.0 

3 

8.9 

b2l 

12.0 

2 

10.3 

49.9 

10.0 

K3C-ALBION.   ILL. 
Transverse. 


No. 

Breadth, 
inches. 

Depth- 
inches. 

Span- 
inches. 

Load- 
pounds. 

Modulus 

of 

Rupture, 

pounds 

persq.in. 

Av.Mod. 

Var. 
from  av. 

Per  cent 
var. 

IRemarks 

2.'.'.'.'. 

3 

4 

5 

6 

7 

8 

9 

3.15 
3.30 
3.20 
3.40 
3.20 
3.15 
3.18 
3.15 
3.30 

3.85 
3.80 
4.00 
3.55 
4.00 
3.85 
3.80 
3.80 
3.78 

6 
6 
6 
6 
6 
6 
6 
6 
6 

Average 

10650 
12830 

4700 
12470 

8360 
14710 

8950 
14100 
11330 

2050 
2420 
830 
2610 
1470 
2810 
1760 
2800 
2160 

2100 

—50 
+320 
-1270 
+510 
-630 
+740 
—340 
+700 

+60 

2.4 
15.2 
60.5 
24.3 
30.0 
35  3 
16  4 
33.3 

2.9 

220.3 

Fracture 
glassy  on 
one  side. 

98100 

18940 

10900 

2100 

24.5 

—6  G 


82 


PAVING    BRICK    AND    PAVING    BRICK   CLAYS.  [bull.  no. 

Table  No.  5—  Continued. 

Absorption. 


Number. 

Kilos. 

Dry. 

Wet 

Gain. 

Per  cent. 

dJ 

3.165 

3.02 

2.9 

3.26 

2.775 

3.23 
3.145 
3.055 
3.34 

2.875 

.065  ' 

.125 

.155 

.08 

.10 

Av 

2.1 
4.1 
5.3 
2.5 
3  6 

2 

3 

c2l 

9 

17.6 

3.5 

Crushing. 


Number. 

Size- 
inches. 

Area- 
square  inches. 

Load- 
pounds. 

Stress 
lb.  per  sq.  in. 

2 

3%x3% 
Ws  x  3% 
3%x3 

m  x  2V2 
m  x  3^ 

3%x4% 

10.9 
11.3 
10.1 

8.4 
10.5 
16.0 

39400 
42000 
63700 
37200 
..51200 
66600 

3600 

4 

3700 

5 

6300 

8 

4430 

9 

4870 

9 

4160 

27060 

Av 4510 

K3d— ALBION,  ILL. 
Transverse. 


No. 


Breadth- 
inches. 


Depth- 
inches. 


Span- 
inches. 


Load- 
pounds. 


Modulus 

of 
Rupture- 
pounds 
per  sq. in. 


Av.Mod, 


Variation 

from 
average. 


Per  cent 
variation. 


1 

2, 
3, 

4 
5 


3.20 
3.20 
3.20 
3.15 
3.10 


Av  .... 


12380 
14450 
9300 
9880 
12350 

58360 

11672 


2520 
2840 
1860 
1960 
2550 

11730 

2350 


2350 


+170 
+490 
-490 
—390 
+200 


7.2 
20.8 
20.8 
16.6 

8.5 

73.9 
14.8 


TESTS   OF    PAVING    BRICK. 

Table   5— Continued. 
Absorption*. 


83 


Kilos. 

Number. 

Dry. 

Wet. 

Gain. 

Per  cent. 

, 

2.88 

2.96 

2.96 

3.045 

2.98 

2.93 

2.975 

2.975 

3.08 

3.02 

.05 

.015 

.015 

.035 

.04 

Average 

1  7 

•> 

0.5 

3 

0.5 

4..    ..            

1  2 

1.3 

5.2 

1.0 

Crushing. 


Numbei 

Size- 
inches. 

Area- 
square  inches. 

Load- 
pounds. 

Stress- 
lbs,  per  sq.  in. 

1 ^T.'tU 

11.4 
10.6 
11.8 
11.4 
11.0 
13.0 

61000 
68000 
58200 
34400 
35100 
78300 

Average 

5350 

3 

I            y!4  x  3J4 

6420 

4 

!         314  x  3^ 

4930 

5 

5 

I             3V2  x  3% 

3U  x  338 

3000 
3200 

3 

1             3M  x  4 

6020 

28920 

4820 

K3e-ALBIOL\T,  ILL. 
Transverse. 


No. 

Breadth—     Depth- 
inches.     J    inches. 

Modulus 

Span—        Load—      Rnn?.f,r„_ 
inches.  ;    pounds.     R^unds 

per  sq.  in. 

Av.Mod. 

Variation 

from 
average. 

Per  cent 
variation. 

1 

9 

3.20    i           3.80 
3.18     |            3.72 
3.18                3  76 

6              10300 
6              13960 
6              14860 
6               15650 

2070 
2860 
2970 
3060 
2540 
2700 

2700 

-630 
+160 
+270 
+360 
—160 

23.3 
5.9 

3...    . 

10.0 

4 3.20     t            3.80 

13.3 

5 3  20                3.70 

6 
6 

A v  .... 

12360 
13930 

5  9 

6 3.18                3.82 

0                         0 

81360 

16200 

58.4 

13560 

2700 

9.7 

84 


PAVING    BRICK    AND    PAVING    BRICK   CLAYS.  [bull.  no.  9 

Table  5 — Continued. 
Absorption. 


Kilos. 

Number. 

Dry. 

Wet. 

Gain. 

Per  cent. 

1... 

2  84 
2.785 
2.915 
2.84 
2.92 

2.875 

2.81 

2.93 

2.86 

2.925 

.035 

.025 

.015 

.02 

.005 

1  2 

2 

0  9 

3 

0  5 

4 

0  7 

5 

0  2 

3.5 

Crushing. 


Number. 

Size- 
inches. 

Area- 
square  inches. 

Load- 
pounds. 

Stress- 
lbs,  per  sq.  in. 

1 

3Mx3 

3H  x  3H 

VA  x  2% 

m  x  m 

9.7 
10.6 

9.3 
12.2 
13.4 

29700 
45400 
26700 
41400 
35800 

Average 

2960 

2.... 

4280 

4 

2880 

6 

3380 

6 

2670 

16170 

3234 

Kjb-ALTON,  ILL. 
Absorption. 


Kilos. 

Number. 

Dry. 

Wet. 

Gain. 

Per  cent. 

bxl 

1.28 
1.08 
1.07 
1.79 
1.875 

1.435 

1.215 

1.205 

1.98 

2.025 

.155 

.135 

.135 

.19 

.15 

Average 

12.1 

12.5 

3 

12.6 

b2l 

10.6 

22 :: :.:.:....... 

8.0 

55.8 

11.2 

TALBOT] 


TESTS    OF    PAVING    BRICK. 

Table  5 — Continued. 

K.c-ALTON,   ILL. 
Transverse. 


85 


No. 

Breadth- 
inches. 

Depth- 
inches. 

Span- 
inches. 

Load- 
pounds. 

Modulus 
of 

Rupture- 
pounds 

per  sqr.  in. 

Av.Mod. 

Variation 

from 
average. 

Per  cent 
variation. 

1 2.85 

2  .              2  70 

3  .              2  82 

3.90 
3.78 
3.85 
3.60 
3.75 
3.68 

6 
6 
6 
6 
6 
6 

Average 

8030 
8390 
5770 
8120 
6480 
6200 

1660 
1960 
1240 
1980 
1440 
1500 

1630 

+  30 
+330 
—390 
+350 
—190 
-130 

1.8 
20.2 
23.9 

4                       2  85 

21.5 

5        .              2  88 

11.7 

6        .              2  74 

8.0 

42990 

9780 

97.1 

7165 

1630 

16.2 

Absorption. 


Kilos. 

Per  cent. 

Number. 

Dry. 

Wet. 

Gain. 

c,l 

2.53 

2.08 

1.945 

1.945 

2.44 

2.63 
2.23 
2  085 
2.035 
2.555 

.10 
.15 
.14 
.14 
.115 

Average 

4.0 

y:::;:;;::;:::: .;;:::::::::......: 

7.2 

7.2 

2 

7.2 

9 

4.7 

30.3 

6.1 

Crushing. 


Number. 

Size- 
inches. 

Area- 
square  inches. 

Load- 
pounds. 

Stress- 
lb.  per  sq.  in. 

1 

2^x4 

2%x4i£ 
2%  x  414 

2^x4 

11.0 
11.7 
11.7 
11.7 

11.0 

47800 
41000 
52000 
33000 
55800 

Average 

4350 

1 

3500 

3 

4440 

5 

2820 

5 

5070 

20180 

4036 

86 


PAVING    BRICK    AND    PAVING    BRICK   CLAYS. 

Table  5 — Continued. 


fBULL.   NO.  9 


K.d-ALTON,   ILL 
Transverse. 


No. 

Breadth- 
inches. 

Depth- 
inches. 

Span- 
inches. 

Load- 
pounds. 

Modulus 
of 

Rupture- 
pounds 

per  sq. in. 

Av.Mod. 

Variation 

from 
average. 

Per  cent 
variation. 

1 

2 

2.75 
2.78 
2.70 
2.78 
2.70 
2.70 

3.68 
3.70 
3.85 
3.70 
3.85 
3' 80 

6 
6 
6 
6 
6 
6 

Average 

8580 
11420 
11100 
13020 

9860 
11330 

65310 

2080 
2700 
2500 
3100 
2220 
2610 

2535 

-4.K 
+165 

-32 
+565 
-315 

+75 

18.0 
6.5 

3 

1.4 

4 

22  3 

5 

12.4 

6 

3.0 

15210 

63.6 

10885 

2535 

10  6 

Absorption. 


Kilos. 

Per  cent. 

Number. 

Dry. 

Wet. 

Gain. 

dxl             ...    . 

2.795 

2.815 

2.64 

2.925 

2.655 

2.82 

2.83 

2.675 

2.955 

2.68 

.025 

.015 

.025 

.03 

.025 

A  verage  .... 

0  9 

2 

0  5 

3 

1  0 

d,l 

1  0 

2 

0.9 

4.3 

0.9 

Crushing. 


Number. 

Size- 
inches. 

Area- 
square  inches. 

Load- 
pounds. 

Stress- 
lb.  per  sq. in. 

1 

3%  x  3 

3|  x  2^ 
3^x2% 
3%  x  2% 
3Mx3 

11.2 
10  3 
10.0 
10.3 
11.2 

87700 
112000 
99000 
58000 
92300 

Average 

7850 

2 

10800 

4...            

9600 

6 

5600 

6.. 

8250 

42100 

8420 

TALBOT] 


TESTS   OF    PAVING    BRICK. 


87 


Table  5 — Continued 


K.e-ALTON,  ILL. 
Transverse. 


Vrt     Breadth, 
iNo-     inches. 

Depth—    Span—  ;    Load- 
inches,      inches,     pounds. 

Modulus 

of 
Rupture, 
pounds 
per.sq.  in 

Av.Mod. 

Var. 
from  av. 

Per  cent 
var. 

Remarks. 

1 2.90 

2                    2  90 

4.48 
4.20 
4.15 
3.90 
3.80 

6 
6 
6 
6 
6 

Average 

7800 
9940 
9t>50 

6290 
6380 

1200 
1750 

1080 
1240 
1220 

1420 

-220 
+350 
+260 

15.5 

24.6 
18.3 

Very 

irregular 

and 

3. ..               3  02 

4                      3  00 

—130            12.7 
—200  I 

badly  out 

5 

3.25 

of 

shape. 

40060 

7090 

85.2 

8012 

1420 

17.0 

Absorption. 


Number. 


Per  cent. 


e,l 

2.49 

2.495 

2.435 

2.27 

2.38 

2.515 

2.525 

2.455 

2.3 

2.415 

.025 

.03 

.02 

.03 

.085 

Average 

1  0 

2 

1.2 

3 

0.8 

e2l 

1.3 

2 

1.5 

5.8 

1.2 

B2b-ATCHISON,   KAN. 
Transverse. 


No. 

Breadth- 
inches. 

Depth- 
inches. 

Span- 
inches. 

Load- 
pounds. 

Modulus 

of 
Rupture- 
pounds 
per  sq.  in. 

Average 

Variation 

from 
average 

Percent 
variation. 

f 

2.46 
2.46 
2.46 
2.46 
2.52 
2.46 
2.46 
2.50 
2.52 
2.46 
2  46 
2.52 

3.90 
3.93 
3.90 
3.90 
3.90 
3.82 
3.84 
3.94 
3.90 
3.84 
3.84 
3.84 

6 
6 
6 
6 
6 
6 
6 
6 
6 
6 
6 
6 

Av  .... 

8140 
6950 
6750 
7920 
9000 
6650 
6110 
5940 
7920 
8950 
6300 
8670 

1960 
166O 
1630 
1910 
2120 
1670 
1520 
1380 
1860 
2220 
1560 
2100 

1S00 

+160 
—140 
-170 
+110 
+320 
—130 
—280 
—420 
+  60 
+420 
—240 
+300 

8.9' 
7  8' 

3  .... 

9  5< 

4  .... 

6  1 

T 

17  8 

b  .... 

7  2 

7  .... 

15  6 

8  .... 

23  4 

9  .... 

3  3 

10  .... 

23  4 

11  .... 

13  3 

12  .... 

16  7 

89300 

21590 

153.0- 

7440 

1800 

12  T 

88 


PAVING    BRICK    AND    PAVING    BRICK    CLAYS. 

Table  5 — Continued. 

F^-ATCHISON,  KAN. 
Absorption. 


Tbull.  no.  9 


Number. 

Kilos. 

Dry. 

Wet. 

Gain. 

Per  cent. 

Bxl 

1.926 

1.882 
2.105 
2.032 
2.42 

2.175 
2.155 

2.385 
2.325 
2.695 

.249 

.273 

.28 

.293 

.275 

Average 

12.9 
14.5 
13.3 
14.2 
11.3 

66.2 

9 

3 

B21 

2 

13.2 

K15b-BARR  CLAY  CO.,  STREATOR,  ILL. 
Transverse  Test. 


No. 

Breadth- 
inches. 

Depth- 
inches. 

Span- 
inches. 

Load- 
pounds. 

Modulus 

of 
Rupture- 
pounds 
persq.in. 

Av.Mod. 

Variation 

from 
average. 

Per  cent 
variation. 

1.... 
2 

3.36 
3.36 
3.36 
3.36 
3.34 
3.34 
3.38 
3.38 
3.34 
3.42 

4.02 
3.96 
4.06 
4.02 
4.06 
4.08 
3.98 
4.08 
3.91 
4.14 

6 
6 
6 
6 
6 
6 
6 
6 
6 
6 

Average 

10400 
10950 
11580 
11800 
11250 
10350 
11360 

9790 
11100 

8980 

1724 

1870 
1881 
1956 
1847 
1675 
1911 
1558 
1959 
1379 

1776 

-  54 
+  94 
+105 
+180 
+  71. 
-101 
+135 
—218 
+183 
-397 

3.4 
5  3 

3 

5  9 

4 

10  1 

5 

4.0 

6.... 

5.7 

7 

7  6 

$     . 

12.3 

9  ... 

10.3 

10... 

22.4 

107560 

17760 

87.0 

10756.0 

1776.0 

8.70 

Absorption. 


Kilos. 

Number. 

Dry. 

Wet. 

Gain. 

Per  cent. 

Bil 

2.965 
2  915 
2.88 
2.808 
3.025 

3.155 
3.145 
3.105 
3.035 
3.275 

.19 

.23 

.225 

.227 

.25 

Average 

6.4 

9 

7.9 

3 

7.8 

B„l 

8.1 

-2.: ::::::: 

8.3 

38.5 

7.7 

TALBOT] 


TESTS   OF    PAVING    BRICK. 

Table  5 — Continued. 
Crushing. 


89 


X7       .                            Size- 
Number,                     inches. 

Area- 
square  inches. 

Load- 
pounds. 

Stress- 
lbs,  per  sq.  inch. • 

3 

4 

5 

7 

8 

33£x2^ 

3%x3 

3::sx2^ 

3%x2^ 

3%x2?4 

8.4 
10.0 
8.4 
8.4 
9  3 

60C00 
68600 
84000 
66C00 
67500 

7150 
6860 
10000 
7850 
7250 

39110 

Average 7822 

K15d-BARR  CLAY  CO.,  STREATOR,  ILL. 
Transverse. 


No. 

Breadth- 
inches. 

Depth- 
inches. 

Span- 
inches. 

Load- 
pounds. 

Modulus 

of 
Rupture- 
pounds 
per  sq.  in. 

Av.Mod. 

Variation 

from 
average. 

Per  cent 
variation. 

1  .... 

2  .... 

3  .... 

4  .... 
5 

6  .... 

7  ... 

8  .... 

9  .... 
10  .... 

3.36 
3.36 
3.36 
3.26 
3.26 
3  30 
3.30 
3.34 
3.30 
3.34 

3.84 
3.84 
3.74 
3.84 
3.82 
3.94 
3.84 
3.78 
3.84 
3  84 

6 
6 
6 
6 
6 
6 
6 
6 
6 
6 

Av  .... 

12990 
12780 
12330 
9800 
11920 
14240 
13700 
13640 
13780 
13270 

2360 
2320 
2360 

1840 
22C0 
2500 
2530 
2580 
2540 
2420 

2365 

—  5 

—  45 

—  5 
—525 
—165 
+135 
+165 
+215 
-175 
+  55 

0.2 
1.9 
0.2 
22  2 
7.0 
5.7 
7.0 
9.1 
7.4 
2.3 

128450 

23650 

63.0 

12845 

2365 

6  3 

K13c— Absorption, 


Kilos. 

Per  cent. 

Number. 

Dry. 

Wet. 

Gain. 

dl 

3.175 

3.29 
3.47 
3.282 
3.315 

3.20 

3.318 

3.51 

3.318 

3.348 

.025 
.028 
.04 

.036 
.033 

Average 

8 

2 

9 

3 

1  2 

c2l 

1  l 

2.::: .. 

1  0 

5.0 

1.0 

90 


PAVING    BRICK    AND    PAVING    BRICK   CLAYS.  [bull.  no.  9 

Table  5 — Continued. 


Number. 


Size- 
inches. 


3 
3 


d%  x  2 
3%  x  2% 

3%  x  iy2 

3%  x  P4 
3%  x  1U 


Crushing. 


Area- 
square  inches. 


6.72 
9.3 
5.5 
4.2 
4.2 


Load- 
pounds. 


Stress- 
lb.  per sq. in. 


56000 
105200 
97100 
37800 
40600 


8360 
11300 
17700 
9000 
9700 


Av. 


56060 
11212 


KI5c-BARR  CLAY  CO.,  STREATOR,  ILL. 

Transverse. 


No. 

Breadth, 
inches. 

Depth- 
inches. 

Span- 
inches. 

Load- 
pounds. 

Modulus 

of 
Rupture, 
pounds 
persq.in. 

Av.Mod. 

Variation 

from 
average. 

Per  cent 
variation . 

1  .... 

2  .... 

3  .   .. 
'4  .... 

5  .... 

6  .... 

7  .... 

8  .... 

9  .... 
10  ... . 

3.34 
3.30 
3.30 
3.24 
3.26 
3.26 
3.24 
3.26 
3.30 
3.30 

3.84 
3.84 
3.78 
3.96 
3.84 
3.90 
3.90 
3.86 
3  84 
3.90 

6 
6 
6 
6 
6 
6 
6 
6 
6 
6 

Av  .... 

14610 
14620 
11870 
14880 
14730 
15600 
12000 
15040 
14270 
13690 

141310 

26702 

2720 

2260 

2640 

2760 

2840 

2200 

2810 

2650 

2490 

2600 

+  70 
+120 
-340 
+  40 
+160 
+240 
-400 
+210 
+  50 
—110 

2.7 
4.6 

13.1 
1.5 
6.2 
9.2 

15.4 
8.1 
1.9 
4.2 

26010 

66.9 

14130 

2600 

6  7 

K15d— Absorption. 


Number. 

Kilos. 

Dry. 

Wet. 

Gain. 

Per  cent. 

D,l 

3.115 

3.005 

3.09 

3.165 

3.255 

3.14 

3.038 

3.105 

3.195 

3.282 

.025 

.033 

.015 

.03 

.027 

Average 

0.8 
1.1 
0.5 
0.9 

0.8 

2 

3 

T>A 

2 

4.1 

0.8 

TALBOTj 


TESTS   OF    PAVING    BRICK. 

Table  5 — Continued. 


91 


Crushing. 


Number. 


[Size- 
inches. 


Area- 
square  inches. 


Load- 
pounds. 


Stress- 
lb.  per  sq. in. 


3 

3%  x  2% 

33s  x  zy2 

m  x  2V2 
3%  x  2% 
3%x3 

8.0 
8.4 
8.4 
8.8 
10.2 

90500 
100800 
109100 
118200 

90800 

11300 

6 

11900 

7 

9 

13000 
13500 

10 

8900 

58600 

Av 11720 

Klse- 


BARR  CLAY  CO.,   STRIiATOR,   ILL. 
Transverse. 


No. 

Breadth- 
inches. 

Depth- 
inches. 

Span-  - 
inches. 

Load- 
pounds. 

Modulus 
of 

Rupture- 
pounds 
per  sq.   in. 

Av.Mod. 

Variation 

from 
average. 

Per  cent 
variation. 

1  ... 

2  .... 

3.36 
3.22 
3.48 
3.36 
3  36 
3.38 
3  30 
3.42 
3.26 
3.36 

3.90 
4.14 
3.98 
3.84 
3.84 
3.90 
3.90 
3.78 
3.84 
3.96 

6 
6 
6 
6 
6 
6 
6 
6 
6 
6 

Av 

17330 
18360 
15110 
14040 
15710 
16020 
19360 
15760 
13580 
18470 

3050 
3000 
2520 
2560 
2860 
2630 
3460 
2960 
2540 
3160 

2870 

-180 
+130 
-350 

—310 

6.3 
4.5 

3 

1^.2 

4 

10.8 

-  10 

—240 
-590 
+  90 
-330 
-290 

0.3 

6  .. 

8.4 

7  .... 

20.6 

8    .. 

3.1 

9  .. 

11.5 

10 

10.1 

163740 

28740 

87.8 

16370 

2870 

8.8 

Absorption. 


Number 


Per  cent. 


e,l  

2.94 

3.17 

3.245 

2.96 

3.01 

2.965 

3.195 

3.275 

2.98 

3.04 

.025 

.025 

.030 

.02 

.03 

Average  .... 

0.8 

2  

.8 

3  

.9 

e->l  

.7 

-2 :::: 

1.0 

4.2 

0.8 

92 


PAVING   BRICK   AND    PAVING   BRICK   CLAYS.  [bull.  no.  9 

Table  5— Continued. 


Crushing. 


Number. 

Size-* 
inches. 

Area- 
square  inches. 

Load—                     Stress- 
pounds,               lb.  per  sq.  in. 

3 

5.... 

3%x2% 
3%x2^ 
3%x2i4 
3%x2^  ' 
3%x2 

8.0 
8.4 
7.6 
9.3 

6.7 

55000 
56900 
78000 
92300 
57200 

Average 

6880 

6..    . 

6780 

8 

10300 

9 

9930 

8550 

42440 



8488 

;b-CANEY,  KAN. 
Transverse. 


No. 

Breadth- 
inches. 

Depth- 
inches. 

Span- 
inches. 

Load- 
pounds. 

Modulus 

of 
Rupture- 
pounds 
per  sq.  in. 

Av.Mod. 

Variation 

from 
average. 

Per  cent 
variation. 

1  . 

2 

2.34 

2.28 
2.16 
2.28 
2  '?2 
2^28 
2.22 
2  22 
2. '28 
2.26 
2.26 
2.21 

4.26 
4.22 
4.21 
4.21 
4.08 
4.21 
4.14 
4.14 
4.08 
4.26 
4.08 
4.08 

6 

6 
6 
6 
6 
6 
6 
6 
6 
6 
6 
6 

Av 

8900 
4940 

11920 
7040 

12250 
8380 
9230 
90.')0 
6170 
7350 
8550 
7700 

1890 
1090 
2830 
1570 
3000 
I860 
2190 
2150 
1460. 
1620 
2050 
1880 

1970 

—  80 

—  880 
+  860 

—  400 
+1030 

—  110 
+  220 
+  180 

—  510 

—  350 
+     80 

—  90 

4.1 
44  6 

3  . 

43  6 

4  . 

20  3 

5  . 

59  o 

6  . 

5  6 

1  . 

11  2 

8  . 

9  . 

9.1 

25  9 

ID  . 

17  8 

11  . 

4  1 

12  . 

4  6 

101480 

23590 

233.1 

8460 

1970 

18  6 

Absorption. 


Number. 

Kilos. 

Dry. 

Wet. 

Gain. 

Per  cent. 

M  

2.39 

2.517 

2.676 

2.42 

2.45 

2.498 

2.63 

2,748 

2.495 

2.505 

.108 
.113 
.072 
.075 
.055 

Average 

4.5 
4.5 
2.7 
3.1 
2.2 

2  

3  

b2l  

2 ::::: 

17.0 

3.4 

TALBOT] 


TESTS    OF    PAVING    BRICK. 

Table  5 — Continued. 


93 


Rab-CAXTON  METROPOLITAN  (Imperial,  i 
Transverse. 


No. 

Breadth—     Depth- 
inches,         inches. 

Span- 
inches. 

Load- 
pounds. 

Modulus 

of 
Rupture- 
pounds 
per  sq.  in. 

Variation 
Av.Mod.        from 
average. 

Percent 
variation. 

1  ... 

2  .. 

3.48 
3. 43 
3.60 
3.54 
3.60 
3.48 
3.48 
3.48 
3.48 
3.48 
3.48 
3.48 

4.02 
4.02 
4.02 
3.96 
3.90 
4.02 
3.96 
3.90 
3.96 
4.02 
3.96 
3.96 

6 
6 
6 
6 
6 
6 
6 
6 
6 
6 
6 
6 

Av 

16130                2580 
16740                26S0 
14680                2270 
20690                3350 
18110                2980 
19770                3170 
15730                2590 
16680                2830 
16970                2800 
19310                 3150 
16640                 2470 
15100                2490 

2800              -220 
—120 

7.9 

4.3 

18.9 

19.6 

6.4 

3 

—530 

4 

—550 

5 

—180 

6  ... 

-370 

13.2 

7 

—210 

7.5 

8  .... 

-  30 

1.1 

9  .... 

0 

0 

10  .. 

—350 

12.5 
2.1 
11.1 

11 

—  60 

12  .... 

—310 

206850              33630 

104.6 

17238                2800 

8.7 

Absorption. 


Kilos. 

Number. 

Dry. 

Wet 

Gain. 

Percent. 

btl  

3.295 
3.975 

4.075 
3.995 
3.775 

3.355 
4.015 
4.105 
4.025 
3.83 

.06 
.04 
.03 
.03 
.055 

Average 

1.8 

2  

0 

1.0 
0.7 

b,l  

0.8 

2  

1.5 

5.8 

1.2 

Crusing. 


Number. 


Size- 
inches. 


Area- 
square  inches. 


Load- 
pounds. 


Stress- 
lb.  per  sq.  in. 


9 

3*4x4 

3^  x  m 
3y2xm 
sy2xiH 

3^x4% 

14. 

14.4 

15.3 

14.9 

15.3 

94550 
109700 

99250 
141700 

83500 

Average 

6750 

3 

6 

7620 
6500 

9500 

1 

5460 

35830 

7166 

94 


PAVING    BRICK   AND    PAVING    BRICK    CLAYS. 

Table  5 — Continued. 

K,b— CANTON,   METROPOLITAN,  (Block). 


[BULL.   NO.  9 


Transverse. 


No. 

Breadth, 
inches. 

Depth- 
inches. 

Span- 
inches. 

Load- 
pounds. 

Modulus 

of 
Rupture- 
pounds 
per  sq.  in. 

Av.Mod. 

Var. 
from  av. 

Per  cent 
variation. 

1  .... 

2  .... 

3.60 
3.54 
3.60 
3.58 
3.58 
3.58 
3.60 
3.54 
3.58 
3.58 
3.54 
3.54 

3.96 
3.96 
3.96 
3.96 
3.96 
3.96 
3.96 
3.90 
3.96 
3.96 
3.90 
3.90 

6 
6 
6 
6 
6 
6 
6 
6 
6 
6 
6 
6 

Average 

19480 
18980 
15480 
18230 
20400 
19830 
21220 
18690 
20770 
17350 
22170 
18870 

3100 
3080 
2470 
2930 
3280 
3180 
3380 
3130 
3320 
2780 
3710 
3170 

3130 

-  30 

—  50 

-660 
-200 
+150 
+  50 
+250 
0 
+190 
-350 
4  580 
+  40 

1.0 
1.6 

3  . . . . 

21.1 

4  .... 

6  4 

5  ... 

4.8 

6  .... 

1.6 

8  0 

8  .... 

0 

9  .... 

6.1 

10  .... 

11.2 

11  .... 

18.5 

12  .... 

1.3 

231470 

37530 

81.6 

19290 

3130 

6.8 

Absorption. 


Kilos. 

Number. 

Dry. 

Wet. 

Gain. 

Per  cent. 

bxl  

3.835 

3.705 

4.12 

3.755 

3.74 

3.885 
3.745 
4.155 
3.785 
3.77 

.05 

.04 

.035 

.03 

.03 

Av 

1.3 

2  

1.1 

3 

0.9 

M  .. 

0.8 

2  

0.8 

4.9 

1.00 

Crushing. 


Number. 

Size 
inches. 

Area 

inches. 

Load- 
pounds. 

Stress- 
lb.  persq.  in. 

10 

3^x4^ 

3^x4 

3^x4^ 

3^x2% 

3^x3Ls 

15.7 
14.0 
14.4 
8.3 
13.6 

126700 
128000 
135800 
58300 
61000 

8070 

4 

5 

9150 
9440 

7 

7030 

8 

4500 

38190 

Av 7638 

TALBOT] 


TESTS    OF    PAY  IN(.    BRICK. 
Table  5 — Continued. 

K13b-CLINTON,  IXD. 
Transverse. 


95 


No. 

Breadth,       Depth- 
inches.     J    inches. 

| 

Span- 
inches. 

Load- 
pounds. 

Modulus 

of 
Rupture—    A  v.  Sr. 
pounds     | 
per  sq.  in. 

Var. 

from  av. 

Per  cent, 
var. 

1  .... 

2 

3.35 
3.48 
3.48 
3.50 
3  38 

4.15 
4.15 
4.22 
4.25 
4  42 

6 
6 
6 
6 
6 

9000 
7410 

11190 
7090 
8670 
7290 
6850 
8000 
9620 

10120 

1100 
1110 
1630 
1010 
1180 
1180 
945 
1110 
1380 
1490 

1240 

+160                  12.9 
—130                  10.5 
+390                  31.4 
—230                  18.5 

-  60                   4.8 

—  60                    4.8 
—295                  23.8 

3  .... 

4  .... 

6  .... 

7  .. 

3.32                4.10                6 
3  40                4.38                 6 

8 

3.52 
3.38 
3.48 

4.30                6 
4.32  |             6 
4.20 

—130                  10.5 

9  .... 
10 

+140                  11.3 
+250 

Av 

85240 

12430 

148.7 

8520 

1240 

14.9 

Absorption. 


Number. 


Kilos. 


Dry 


Wet. 


Gain. 


Per  cent. 


bj    

3.46 

3.678 

3.745 

2.698 

3.81 

2.678 

.218 

.250 

.338 

.22 

.328 

Av 

6.3 

2  

3  

b2l  

3.495 

2.66 

3.59 

7.2 
12.7 

6.1 

2  

2.35 

14.0 

46.3 

9.3 

Crushing. 


Number. 

Size 
inches. 

Area 
inches. 

Load- 
pounds. 

Stress- 
lb.  per  sq. in. 

1 

3%x4 

3%x3% 

3%x4^> 

15. 6* 

11.8 

U.5 

12.2 

15.2 

40100 
19400 
195C0 
36700 
75600 

2580 

6 

1640 

1440 

9 .... 

3000 

10 

5000 

13660 

Av 2732 

96 


PAVING   BRICK   AND    PAVING    BRICK   CLAYS. 

Table  5—  Continued. 

KI3c-CLINTON,   IND. 
Transverse. 


[bull.  no.  9 


No. 

Breadth, 
inches. 

Depth- 
inches. 

Span- 
inches. 

Load- 
pounds. 

Modulus 

of 
rupture,— 

pounds 
persq.  in. 

Av.  Sr. 

Var. 
from  av. 

Percent 
var. 

1 

2 

3 

4 

5 

6 

7 

8 

9 

3.48 
3.36 
3.42 
3.28 
3.36 
3.42 
3.40 
3.42 
3.38 

4.08 
4.21 
4.02 
4.32 
4.10 
4.08 
4.02 
4.16 
4.10 

6 

6 
6 
6 
6 
6 
6 
6 
6 

Average 

8310 
10550 
6850 
9960 
7820 
7720 
7410 
9020 
6310 

1290 
1590 
1120 
1470 
1250 
1220 
1220 
1380 
1000 

1280 

+10 
+310 
-160 
+190 
-30 
—60 
-60 
+100 
—280 

0.8 

24.2 

12.5 

14.8 

2.3 

4.7 

4.7 

7.8 

21.9 

73950 

11544 

93.7 

8220 

1280 

9.4 

Absorption. 


Number. 

Kilos. 

Per  cent 

Dry. 

Wet. 

Gain. 

c,l 

3.308 
3.288 
3  215 
3.265 
3.23 

3.495 

3.512 

3.42 

3.48 

3.525 

.187 
.224 
.205 
.215 
.295 

Av 

5  7 

2 

6.8 

3 

6.4 

c2l 

6.6 

2 

9.1 

34.6 

6.9 

K13d-CLINTON,   IND. 
Transverse. 


No. 

Breadth, 
inches. 

Depth- 
inches. 

Span- 
inches. 

Load- 
pounds. 

Modulus 

of 
rupture,— 

pounds 
per  sq.  in. 

Av.  Sr. 

Var. 
from  av. 

Percent 
var. 

1 

2 

3 

4 

5.... 

6 

7 

8 

10*. '.'.'.'. 

3.20 
3.40 
3.20 
3.28 
3.30 
3.20 
3.25 
3.35 
3.38 
3.15 

4.10 
3.95 
4.05 
4.00 
4.02 
4.10 
4.02 
3.98 
4.10 
3.90 

6 
6 
6 
6 
6 
6 
6 
6 
6 
6 

Average 

10240 

8580 

8640 
11100 

8930 
11620 

5380 
12040 
10040 

8580 

1710 
1460 
1490 
1900 
1510 
1940 
925 
2040 
1590 
1610 

1620 

+90 
-160 
—130 
+280 
—110 
+320 
-695 
+420 
-30 
-10 

5.5 

9.9 

8.0 

17.3 

6.8 

19.8 

42.8 

25.9 

1.9 

0.6 

95150 

16170 

136.5 

9515 

1620 

13.6 

TALBOT] 


TESTS    OF    PAVING    BRICKS. 

Table  5 — Continued. 


97 


Absorption. 


• 

Kilos. 

Per  cent. 

Number. 

Dry. 

Wet. 

Gain. 

d,l 

3.51 

3.575 

3.46 

3.035 

3.768 

3.545 
3.625 
3.545 
3.078 
2.835 

.035 

.05 

.085 

.043 

.067 

Av 

1.0 

9 

1.4 

3  

2.5 

d..l     .                          

1.4 

2 

2.4 

8.7 

1.7 

Crushing. 


Number. 

Size- 
inches. 

Area- 
square  inches. 

Load- 
pound. 

Stress- 
lb.  per  sq.  in. 

5    . 

3%x4 

3%x2^ 

3%x4 

3%x3% 

3%x4 

13.5 
8.4 
13.5 
12.7 
13.5 

54700 
66000 
82300 
54000 
105400 

4050 

6 

7860 

8 

6100 

8 

9 

4250 
7800 

30060 

Av 6012 

K13e-CLlNTON,  IND. 


Transverse. 


No. 

Breadth- 
inches. 

Depth- 
inches. 

1 

1 
Span—        Load- 
inches,      pounds. 

Modulus 

of 
Rupture- 
pounds 
per  sq.  in. 

Av.Mod. 

Variation 

from 
average. 

Per  cent 
variation. 

1 

? 

3.36 
3.38 
3.36 
3.40 
3.36 
3.42 
3.36 
3.36 
3.36 
3.42 

4.20 
4.14 
3.96 
4.26 
4.20 
4.50 
4.08 
4.24 
4.08 
4.02 

6 
6 
6 
6 
6 
6 
6 
6 
6 
6 

Av  ... 

6230 
3430 

10650 

22940 
9450 

12210 
49.50 
6660 

13400 
8200 

950 

530 

1820 

3350 

1440 

1600 

795 

995 

2160 

1350 

1500 

-  550 
970 

+  320 
+1850 

-  60 
+  100 

-  705 

-  505 
+  660 

-  150 

36.7 
64.6 

3 

21.4 

4 

123.2 

5 

4.0 

fi 

6.7 

7 

47.1 

8- 

33  7 

9 

44.1 

10 

10.0 

100120 

14990 

391.5 

10000 

1500 

39.2 

— 1   G 


98 


PAVING    BEICK    AND    PAVING    BRICK   CLAYS. 

Table  5 — Continued. 
Absorption. 


fBULL.   NO.  9 


Kilos. 

Number. 

Dry. 

Wet. 

Gain. 

Per  cent. 

dl 

3.778 
3  363 
3.58 
3.122 
2.91 

3.812 

3.40 

3.62 

3.15 

2.95 

.034 

.037 

.04 

.028 

.04 

Average 

0  9 

9 

1.1 

3 

1.1 

e.,1 

0.9 

2  ... 

1.4 

5.4 

1  1 

Crushing. 


Number. 

Size- 
inches. 

Area- 
square  inches. 

Load- 
pounds. 

Stress- 
lbs,  per  sq. in. 

2 

3 

5 

9 

3^x3M 

3^x2^ 
3^x4*4 
3V2  x  4V4 
3^x4 

11.4 
9.6 
14.9 
14.9 
14. 

63700 
45400 
71000 
102900 
80700 

Average 

5600 
4740 
4760 
6900 

10    

5760 

27760 

5552 

G2-COFFEYVILLE  BLOCK,  KANSAS. 
Transverse  Test. 


No. 

Breadth- 
inches. 

Depth- 
inches. 

Span- 
inches. 

Load- 
pounds. 

Modulus 

of 
Rupture- 
pounds 
per  sq.  in. 

Av.Mod. 

Variation 

from 
average . 

Per  cent 
variation . 

1  .... 
2 

3.18 
3.12 
3.14 
3.18 

4.02 
3.96 
4.02 
4  02 

6 

6 
6 
6 
6 
6 
6 
6 
6 
6 

Av  .... 

7010 

13580 
12970 

7550 
120H0 

6950 
11370 
10999 
11550 
12880 

1240 
2500 
2320 
1330 
2120 
1220 
2000 
1980 
1990 
2350 

1905 

-665 
+595 
+415 
—575 
+215 
-685 
+  95 
+  75 
+  85 
+445 

34.9 
31.3 

3 

21.8 

4  . 

30.2 

5 

3.18                4  02 

11.6 

6 

3.18 
3.18 
3.18 
3.24 

3.18 

4.02 
4.02 
3.96 
4.02 
3.94 

36.0 

7 

5.0 

8 

4.0 

9 

4.5 

10 

23.4 

106940 

19050 

202.7 

10694 

1905 

20.3 

Absorption. 
(See  Coffeyville  "Brick.") 


TALBOT] 


TESTS   OF    PAVING    BRICK. 

Table  5 — Continued. 

G2-COFFEYVILLE  BRICK,  KANSAS. 


99 


Transverse  Test. 


No. 

Breadth- 
inches. 

Depth- 
inches. 

Span- 
inches. 

Load- 
pounds. 

Modulus 

of 
Rupture- 
pounds 
per  sq.  in. 

Av.Mod. 

Variation 

from 
average. 

Per  cent 
variation. 

1  .... 

9 

2.16 
2.14 

2.28 
2.18 
9  99. 

3.84 
3.78 
3.84 
4.14 

3.89 
3.84 
3.84 
3.82 
3.84 
3.84 
3.88 
3.84 

6 
6 
6 
6 
6 
6 
6 
6 
6 
6 
6 
6 

Av  .... 

8890 
9040 
7520 
7960 
10630 
8490 
8610 
7670 
8000 
7780 
8800 
8940 

2511 
2659 
2014 
1918 
2844 
2398 
2370 
2171 
2105 
2141 
2371 
2395 

2325 

+186 
-334 
—311 
—407 
+519 

8.0 
14.4 

3 

13.4 

4 

17  5 

5 

22.3 

6                     2  16 

+  73 
+  45 

3  1 

7                    •>  22 

1.9 

8                       2  18 

-154 
-220 
—184 

+  46 
-  70 

6  6 

9 

2.32 
2.22 
2  22 
2.28 

9  5 

10 

7.9 

11 

2.0 

12  .. 

3.0 

1023?0 

27897 

109.6 

8528 

2325 

9.1 

Absorption 


Kilos. 

Number. 

Dry. 

Wet. 

Gain. 

Per  cent. 

b,l 

2.45 

2.322 

2.49 

2.46 

2.408 

2.465 

2.35 

2.51 

2.475 

2.425 

.015 

.028 

.02 

.015 

.025 

Average 

0.0 

9 

1.6 

3 

0.2 

b,l 

0.8 

2 

1.6 

4.2 

0.8 

Crushing. 


Number. 


Size- 
inches. 


Area- 
square  inches. 


1 
2 
2 
9 
10 


?,H  x  3:;. 
3i  i  x  4 
314x4 
31/2XI 
3^x3^ 


Load- 
pounds. 


Stress- 
lbs,  per sq. in. 


11 

73700 

13 

65000 

13 

94700 

13 

79000 

11.4 

82500 
Average 

6700 
5000 
7300 
6080 
7250 

32330 


100 


PAVING    BRICK    AND    PAVING   BRICK   CLAYS. 

Table  5 — Continued. 


[BULL.   NO.  9 


FlC-DANVILLE  BRICK  CO.,  DANVILLE,  ILL. 
Transverse. 


No. 

Breadth- 
inches. 

Depth- 
inches. 

Span- 
inches. 

Load- 
pounds. 

Modluus 
of 
Rupture- 
pounds 
per  sq    in. 

Av.Mod. 

Variations 

from 
Average. 

Per  cent 
Variation. 

1 

2 

3  24 
3.18 
3.24 
3.22 
3.18 
3.14 
3.15 
3.13 
3.24 
3.24 

4.20 
3.98 
4.20 
4.20 
4.02 
4.08 
4.10 
3.96 
4.14 
4.08 

6 
6 
6 
6 
6 
6 
6 
6 
6 
6 

Average 

9890 
11540 
8980 
8460 
11290 
10970 
11420 
8090 
9100 
11370 

1560 
2060 
1420 
1340 
1980 
1890 
1950 
1480 
1480 
1890 

1700 

—140 

+360 
—280 
—360 
+280 
+190 
+250 
—220 
—220 
+190 

8.2 
21.2 

3 

16.5 

4 

21.2 

5 

16.5 

6 

11.2 

7 

14.7 

8.... 

12.9 

9 

12.9 

10 

11.2 

101110 

17050 

146.5 

10110 

1700 

14. & 

Absorption. 


Number. 

Kilos. 

Dry. 

Wet. 

Gain. 

Per  cent. 

dl 

2.94 

3.015 

3.23 

2.085 
3.155 

3.115 

3.15 

3.322 

2.23 

3.275 

.175 
.135 
.092 
.145 
.12 

Average  

6.0 

2 

4.5 

3..                    

2.9 

c,l 

7.0 

22. ::::::::::::::::::: 

3.8 

24.2 

4.8 

Crushing. 


Number. 

Size- 
square  inches. 

Area- 
inches. 

Load- 
pounds. 

Stress- 
lb.  per  sq. in. 

1 

3^4  x  3 
3H  x  2VA 
3V4  x  2% 
3V4  x  2% 
31/4  x  3 

9.7 
7.3 
8.9 
8.5 
9.7 

39900 
48800 
37700 
42300 
58900 

4100 

4 

6700 

6 

4240 

6. . . .                  .... 

5000 

10 

6100 

26140 

Average  ....5228 

TALBOT] 


TESTS   OF    PAVING    BRICK. 

Table  5 — Continued. 

F,d-DANVILLE  BRICK  CO..  DANVILLE,  ILL. 
Transverse. 


101 


No. 

Breadth—     Depth- 
inches,         inches. 

Span- 
inches. 

Load 
pounds. 

Modulus 

of 
Rupture—  Av.Mod. 

pounds    j 
per  sq.  in.1 

Variation 

from 
average. 

Per  cent 
variarion. 

2. 

3.34 
3.48 
3.46 
3.34 
3.36 
3.34 

4.24 
4.26 
4.52 
4.10 
4.20 
4.14 

6 
6 
6 
6 
6 
6 

4970 
7180 
3000 
7690 
8560 
6910 

745 
1020 

420 
1240 
1310 
1090 

980 

-235 
+40 
-560 
—260 
+330 
+110 

24.0 
4  1 

3. 

57  2 

4. 

26  6 

5. 

33.7 

6. 

11.2 

7.     . 

8. 

3.30 
3.30 
3.36 

4.32 

4.26 
4.08 

6 
6 
6 

Av 

4700 
5  tOO 
9090 

690 

815 

1460 

-290 
—165 
^480 

29  6 

9. 

16.8 

10. 

49.0 

57500 

8790 

242.2 

6370 

980 

26.9 

Absorption. 


Kilos. 

Number. 

Dry. 

Wet. 

Gain. 

Per  cent. 

dil 

2.955 

3.16 

3.18 

3.09 

3.292 

3.03 

3.268 

3.285 

3.185 

3.352 

.078 
.108 
.105 
.095 
.06 

Average  ..... 

2.6 

2.                             

3.4 

3 

3  3 

d2l 

3.1 

3 

1.8 

14.2 

2.8 

Crushing. 


NUMBER.                            Sgf- 

Area—                      Load- 
square  inches.               pounds. 

Stress- 
lb.  per sq. in. 

6 

6 

3%  x  4V2 
3%x4i& 
m  x  4M 
3%x4% 
'&XA  x  3% 

15.2 
14.3 
14.3 
14.7 
12.2 

60300 
43400 
55400 
37400 
40100 

4000 
3040 

it 

3880 

9.. 

2550 

10 

3280 

16750 

Average  ....  3350 

102 


PAVING    BRICK    AND    PAVING   BRICK    CLAYS. 

Table  5 — Continued. 


[BULL.  NO.  9 


Fxe-DANVILLE  BRICK  CO.,  DANVILLE,  ILL. 
Transverse. 


No. 

Breadth- 
inches. 

Depth- 
inches. 

Span- 
inches. 

Load- 
pounds. 

Modulus 

of 
Rupture- 
pounds 
persq.in. 

Av.Mod. 

Variation 

from 
average. 

Per  cent 
variation. 

2 

3.36 
3.36 
3.24 
3.30 
3.24 
3.42 
3.36 
3.42 
3.42 
3.48 

4.08 
3.96 
3.72 
3.84 
3.96 
4.20 
4.08 
3.96 
4.32 
4.44 

6 
6 
6 
6 
6 
6 
6 
6 
6 
6 

14380 

12650 

8160 

9500 

6330 

13190 

11440 

7890 

12260 

6130 

2300 
2160 
1640 
1760 
1120 
.     1980 
1810 
1330 
1740 
805 

1670 

+630 
+490 
—  30 
+  90 
-550 
+310 
+170 
—340 
+  70 
-865 

37.7 
29.4 

3 

1.8 

4 

5.4 

5 

32.9 

6 

18.6 

10.2 

8 

20.4 

9 

4.2 

10 

51.8 

101930 

16675 

212.4 

10190 

1670 

21.2 

Absorption. 


Kilos. 

Number. 

Dry. 

Wet. 

Gain. 

Percent. 

e,l 

2.92 

3.105 

2.75 

2.92 

2.81 

2.96 

3.135 

2.79 

3.005 

2.85 

.04 

.03 

.04 

.085 

.04 

Average 

1.4 

2 

1.0 

3 

1.5 
2.9 

9 

1.5 

8.3 

1.7 

Crushing. 


Number. 

Size- 
square  inches. 

Area- 
square  inches. 

Load- 
pounds. 

Stress- 
lb.  per sq. in. 

1  

3^x2^ 
3i4x2 
314  1  2 
3M  x  2 
3Mx  2 

8.1 
6.5 
6.5 
6  5 
6.5 

41300 
34200 
50900 
43200 
36000 

5100 

6  

5260 

6 

7830 

7  

6650 

9  

5550 

30390 

Average 6078 

TESTS    OF    PAVING    BRICK. 

Table  5 — Continued. 


103 


K5b-EDWARDSVILLE. 
Absorption. 


Kilos. 

Number. 

Dry. 

Wet. 

Gain. 

Percent. 

b  l  

8.67 

2 

10.71 

3      

10.36 

b2l                        

8.79 

2 ■ 

9.60 

48.13 

K5c 
c   1 

Average  ..9.62 
7.37 

2 

5.90 

c   1 

3.52 

2    

3.84 

3                                

2.79 

23.42 

K5d 
d2l 

Average  .4.68 
2.42 

22 

2.86 

d  1 

2.71 

2 

2.59 

3  .             

2.54 

13.12 

K5e 
e2l  

Average  ..2.62 
1  93: 

1.34 

e  1 

1.49 



0.7T 

3 

1  3T 

6.90 

Average  ..1.38 

104 


PAVING    BRICK    AND    PAVING    BRICK   CLAYS. 

Table  5 — Continued. 

K2b-HYDRAULIC,  ST.  LOUIS,  MO. 
Transverse. 


[BULL.  NO.  9 


No. 

Breadth, 
inches. 

Depth- 
inches. 

Span- 
inches. 

Load- 
pounds. 

Modulus 

of 

Rupture, 

pounds 

per  sq.in. 

Av.Mod. 

Var. 
from  av. 

Per  cent 
var. 

Remarks 

1... 
2... 

2.88 
2  82 
2.80 
2.88 
2.86 
2.76 
2.78 
2.96 
2.80 
2.85 
2.78 
2.88 

3.90 
3.84 
3.94 
3.88 
3.96 
3.84 
4.04 
3.80 
4.05 
3.95 
4.05 
4.10 

6 
6 
6 
6 
6 
6 
6 
6 
6 
6 
6 
6 

Average 

11970 
11810 
15750 
16780 
1H090 
103  JO 
17380 
14150 
5610 
6060 
14370 
4640 

2460 
2570 
3250 
3480 
2640 
2290 
3430 
29S0 
1100 
1230 
2830 
860 

2430 

+    30 
+  140 
+  820 
+1050 
-f   210 
—  140 
+1000 
+  550 
-1330 
+1200 
+  400 
—1570 

1.2 

5.8 

33.7 

43.2 

•       8.6 

5.8 
41.1 
22.6 
54.6 
49.3 
16.5 
64.6 

3... 

4... 

5.... 

6.... 

7... 

8.... 

9... 

10... 

11.... 

12.... 

glazed. 

141950 

29120 

347.0 

11830 

2430 

28.9 

Absorption. 


Kilos. 

Number. 

Dry. 

Wet. 

Gain. 

Per  cent. 

bxl 

3  005 

3.23 

3.235 

3.12 

3.32 

3.025 

3.24 

3.275 

3.13 

3.33 

.02 
.01 
.04 
.01 
.01 

Average 

0  7 

2 

0  3 

3 

1  2 

b,l 

0  3 

0.3 

2.8 

0.6 

Crushing. 


Number. 

Size- 
square  inches. 

Area- 
inches. 

Load- 
pounds. 

Stress- 
lb.  per  sq. in. 

11    

11    

2%  x  mi 
2?s  x  m 
2?8  x  m 

2%  x  V-A 
2%  x  3M 

10.8 
10.8 

9.3 
10.0 

9.3 
10.0 

76200 
69800 
107500 
77900 
80500 
75400 

Average 

7560 
6940 

7    

11500 

2    

7790 

10    

8650 

9    

7540 

49980 

8330 

TALBOT] 


TESTS    OF    PAVING    BRICK. 

Table  5 — Continued. 


105 


K^b-INDIANA  BLOCK,  BRAZIL,  IND. 
Transverse. 


Modulus 

No. 

Breadth, 
inches. 

Depth- 
Inches. 

Span- 
inches. 

Load- 
pounds. 

of 
Rupture, 
pounds 

A--Mod-fromrav. 

Per  cent 
var. 

Remarks. 

1 

persq. in 

1... 

3.30 

4.35 

6 

4940 

715 

685 

+30 

4,4 

9 

3.35 

4.40 

6 

6670 

930 

+245 

35.8 

3 

3.35 

4.30 

6 

4280 

620 

—65 

9.5 

4... 

3.35 

4.40 

6 

3780 

525 

+160 

23.4 

5... 

3.35 

4.34 

6 

5000 

715 

+30 

4.4 

6... 

3.40 

4.30 

6 

3040 

435 

-250 

36.5 

7     . 

3.35 

4.38 

6 

6030 

845 

+160 

23.4 

8 

3  30 

4  35 

6 

5180 

745 

+  60 

8.8 

9 

3.32 

4.42 

6 

7770 

1080 

+395 

57.6 

10... 

3.30 

4.32 

6 
Average 

1740 

255 

-430 

62.8 
266.6 

Break 

48130 

6865 

4840 

685 

26.7 

Absorption 


Kilos. 

Number 

Dry. 

Wet 

Gain. 

Per  cent. 

bxl 

2 

1.5 
1.395 
2  528 
2.005 
2.398 

1.745 

1.602 

2.83 

2.235 

2.665 

.245 

.207 

.302 

.23 

.267 

Av 

16.3 
14.8 

3. 

11  9 

b,t...                      

11.5 

•? 

11.1 

65  6 

13.1 

K,  ^-INDIANA  BLOCK,  BRAZIL,  IND. 
TRANSVERSE 


Modulus 

No. 

Breadth, 
inches. 

Depth- 
inches. 

Span- 
inches. 

Load- 
pounds. 

of 

Rupture, 

pounds 

persq.in. 

Av.Mod. 

Var. 

from  av. 

Per  cent 
var. 

! 

3.18 

3.94 

6 

10850 

1980 

1510 

+470 

31.2 

2.... 

3.18 

3.84 

6 

7650 

1470 

-40 

2.6 

3.... 

3.16 

3  98 

6 

8340 

1510 

0 

0 

4.... 

3.10 

3.96 

6 

7000 

1300 

—210 

13.9 

o 

3.12 

3.95 

6 

6950 

1280 

-230 

15.2 

6.... 

3.24 

4.18 

6 

8320 

1320 

-190 

12.6 

7.... 

3.12 

3.96 

6 

8330 

1540 

+30 

2.0 

8.... 

3.12 

4.02 

6 

7600 

1360 

-150 

9.9 

9.... 

3.18 

3.86 

6 

9280 

1760 

+250 

16.6 

10.... 

3.18 

3.90 

> 

6 
Average 

8060 

1610 

+100 

6.6 

82980 

15130 

110.6 

8300 

1510 

11.1 

KM) 


PAVING    BRICK    AND    PAVING    BRICK   CLAYS. 

Table  5 — Continued. 
Absorption. 


[BULL.   NO. 


Kilos. 

Number. 

Dry. 

Wet. 

Gain. 

Percent. 

c,l 

2.938 
3  18 
3.003 
2.993 
3.11 

3.062 

3.23 

3.095 

3.10 

3.185 

.124 

.05 

.092 

.097 

.075 

Av 

4.2 

% 

1.6 

3 

3.1 

c2l 

3.2 

2 

2.4 

14.5 

2.9 

Klld-INDIANA  BLOCK,  BRAZIL,  1ND. 

Transverse. 


No. 

Breadth- 
inches. 

Depth- 
inches. 

Span- 
inches. 

Load- 
pounds. 

Modulus 
of 

Rupture- 
pounds 

per  sq.  in. 

Av.Mod. 

Variation 

from 
average. 

Per  cent 
variation. 

1.... 
2     . 

3.18 
3.14 
3.14 
3.14 
3.15 
3.22 
3.10 
3.15 
3.10 
3.20 

3.90 
3.90 
3.90 
4.05 
3.94 
3.85 
3.94 
4.00 
3.95 
3.98 

6 
6 
6 
6 
6 
6 
6 
6 
6 
6 

Av  . . . . 

10490 
10500 
10680 
13980 
12140 
12850 
11960 
13950 
13670 
12450 

1960 
1980 
2020 
2450 
2250 
2430 
2240 
2500 
2540 
2220 

2260 

-300 
—280 
—240 
+190 

—  10 
+170 

—  20 
+240 
+280 

—  40 

Av 

13.3 
12.4 

3 

10.6 

4 

8.4 

5... 

0.4 

6 

7.5 

7     . 

0.9 

8     . 

10.6 

9 

12.4 

10 

1.8 

122670 

22590 

78.3 

12270 

2260 

7.8 

Absorption. 


Kilos. 

Number. 

Dry. 

Wet. 

Gain. 

Per  cent. 

d,l 

2.955 
.      2.96 
2.95 
3.025 
3.045 

3.008 
3.015 
3.002 
3.075 
3.10 

.053 
.055 
.052 
.050 
.055 

Average 

1.8 

9 

1.9 

3 

1.8 

d.,1.  ..              

1.7 

2 

1.8 

9.0 

1.8 

TALBOTj 


TESTS    OF    PAVING    BRICK. 

Table  5 — Continued. 


107 


Klle-IN DIANA  BLOCK.  BRAZIL,   IND. 
Transverse. 


No. 

Breadth- 
inches. 

Depth- 
inches. 

Span—      Load- 
inches,     pounds. 

Modulus 

of 
Rupture- 
pounds 
persq.in. 

Ay. 

Mod. 

Varia- 
tion 
from 
average 

Per  cent 
variation 

Remarks. 

1:::: 

3.... 
4.... 
5.... 
6.... 

'» 

8.... 
9.... 
10.... 

3.18 
3.18 
3.30 
3.42 
3.18 
3.24 
3.18 
3.24 
3.24 
3.18 

4.38 
4.20 
4.56 
4.80 
4.38 
4.38 
4.56 
4.68 
4.68 
4  56 

6 
6 
6 
6 
6 
6 
6 
6 
6 
6 

A v  .... 

6480 
9260 
4810 
6220 
8520 
4310 
4040 
4830 
6950 
7350 

955 

1480 

635 

710 

1260 

625 

550 

615 

880 

1000 

870 

+  85 
+610 
-235 
—160 
-390 
-245 
—320 
-255 
+  10 
+130 

9.8 
70.1 
27.0 
18.4 
44.8 
28  2 
36.8 
29.3 

1.1 
14.9 

Overbur'd 

.do 

.  .do 

.  .do 

.  .do 

.  .do 

..do 

.  .do 

.  .do 

.  .do 

62770 

8710 

280.4 

6280 

870 

28.0 

Absorption. 


Number, 


Per  cent. 


e,l 

9 

e?l 
2. 


2.31 

2.33 

2.595 

2.625 

2.675 


2.405 
2.66 
2.678 
2.74 


.08 

.075 

.065 

.053 

.065 


Average 


3.5 

3.2 
2.5 
2.0 

2.4 


13.6 
2.7 


S2b-KANSAS  CITY  DIAMOND. 
Transverse. 


No. 


Breadth, 
inches. 


Depth- 
inches. 


Span- 
inches. 


Load- 
pounds. 


Modulus 

of 
Rupture,  Av.Mod. 
pounds 
persq.in.  I 


Var. 
from  av, 


Per  cent. 

var. 


Remarks. 


1... 

ZM 

3.78 

6 

10480 

2580 

2410 

+170 

7.0 

2.... 

2.46 

3.70 

6 

9590 

2560 

-150 

6.2 

3... 

2.50 

3.66 

6 

9180 

2470 

+  60 

0  2 

4.... 

2.58 

3.72 

6 

11400 

2560 

-150 

6.2 

5.... 

2.46 

3.82 

6 

5010 

1260 

—1150 

47.6 

Over- 

6.... 

2.54 

3.66 

6 

7920 

2090 

-320 

13.6 

burned. 

7.... 

2.46 

3.64 

6 

11620 

3060 

+650 

27.0 

8.... 

2.58 

3.78 

6 

7040 

1720 

-690 

28.6 

9.... 

2.56 

3.72 

6 

9000 

2540 

-130 

5.4 

10.... 

2.52 

3.66 

6 

10050 

2680 

+270 

11.2 

11.... 

2.4*3 

3.72 

6 

10620 

2820 

-410 

17.0 

12.... 

2.52 

3.60 

6 
Average 

9420 

2610 

-2C0 

8.3 

111330 

28950 

178.3 

9280 

2410 

14.9 

108 


PAVING    BRICK    AND    PAVING    BRICK   CLAYS.  [bull.  no.  9 

Table  5 — Continued. 


Absorption. 


Kilos. 

Per  cent. 

Number. 

Dry. 

Wet. 

Gain. 

1  ime. 

b>7l 

2.180 
2.315 
1.805 
2.085 
2.185 

2.200 
2  330 
1.815 
2.095 
2.205 

0.020 
.015 
.010 
.010 
.020 

Av 

0.9 
.6 
.6 
.5 

1.0 

48  hours, 
do 

2.:::::::::::::::: 

3 

do 

b,l 

2 : 

..do 

do 

3.6 

0.7 

L2b-LAWRENCE,   KANSAS. 
Tranverse. 


No. 

Breadth- 
inches. 

Depth- 
inches. 

Span- 
inches. 

Load- 
pounds. 

Modulus 

of 
Rupture- 
pounds 
per  sq.  in. 

Average 
Mod. 

Variation 

from 
average. 

Per  cent 
variation. 

1  .... 

2  .... 

3  ... 

4  .... 

5  .... 

6  .... 

7  .... 

8  .... 

9  .... 
10  ... . 

2.53 

2.55 
2.55 
2.50 
2.53 
2.52 
2.53 
2.50 
2.55 
2.55 

3.61 
3.62 
3.68 
3.52 
3.65 
3.60 
3.65 
3.68 
3.60 
3.65 

6 
6 
6 
6 
6 
6 
6 
6 
6 
6 

Av  .... 

9500 

6500 
F.670 
7200 
6600 
6520 
4870 
5600 
7250 
5550 

2600 
1750 
1470 
2100 
1770 
1800 
1300 
1490 
1970 
1480 

1770 

+830 
—  20 
—300 
+330 
0 
+  30 
-330 
—280 
+200 
—290 

46.8 
1.1 
16.9 
18.6 
0.0 
1.7 
18.6 
15.8 
11.3 
16.4 

652^0 

17730 

147.2 

6530 

1770 

14.7 

. 

Absorption. 


Kilos. 

Per  cent. 

Number. 

Dry. 

Wet. 

Gain. 

bjl 

2.06 

2.175 

2.10 

1.90 

2.215 

2.112 
2.202 
2.142 
1.932 
2.242 

.052 
.027 
.042 
.032 
.027 

Av 

2.5 

2 

1.2 

3 

2.0 

b2l 

1.7 

2 :.. 

1.2 

8.6 

1.7 

TALBOT] 


TESTS    OF    PAVING    B  HICK. 

Table  5 — Continued. 

L,c-LAWRENCE,   KAX. 
Transverse. 


109 


Modulus 

No. 

Breadth, 
inches. 

Depth- 
inches. 

Span- 
inches. 

Load- 
pounds. 

Rupmre-    A  v.  Mod.    froXmarav 
pounds                         rroma%. 
per  sq.  in. 

Per  cent 
var. 

l.... 

2.40 

3.60 

6 

9410 

2730             1960 

-770 

39.3 

2.... 

o  40 

3.55 

6 

7380 

2180 

-220 

11  2 

3.... 

2.50 

3.66 

6 

7120 

1920 

-40 

2.0 

4.... 

25.2 

3.74 

6 

7240 

1860 

—ICO 

5.1 

5 . . . . 

2.48 

3.52 

6 

4S20 

1410 

—550 

28.0 

6.... 

2.48 

3.64 

6 

6100 

1670 

— 290 

14.8 

7. . . . 

2.55 

3.70 

6 

7020 

1810 

—150 

7.6 

8.... 

2.48 

3.70 

6 

7610 

2020 

-60 

3.0 

9.... 

2.47 

3.62 

6 

7090 

19>0 

—20 

1.0 

10.... 

2.50 

3.72 

6 
Average 

7630 

2000 

-40 

2.0 

71220 

19580 

114.0 

7120 

1960 

11.4 

Absorption. 


NUMBER. 


Kilos. 


Dry 


Wet. 


Gain. 


Per  cent. 


c,l 

2.385 

2.408 

2.40 

2.36 

2.47 

2.392 

Av 

.023 
.018 
.02 
.02 
022 

1.0 

2 

2.382 

0.8 

3 

2,34 

0.9 

Col 

2  45 

0.8 

2 

2.37 

0.9 

4.4 

0.9 

Crushing. 


Number. 

Size- 
inches. 

A  re  a— 
square  inches. 

Load- 
pounds 

Strt-s?- 
1b.  per  sq 

in. 

- 

2iox2'4 
2^x2\> 

21 0  x  zh 

6.2 
6.2 
6.2 
6.9 
5.6 

520C0 
58700 
45800 
90(X.0 
67700 

S4C0 

8.. 

9.. 
10.. 
11.. 

9-500 

7400 

13000 

12000 

50300 

Av 

.10060 

110 


PAVING    BRICK    AND    PAVING    BRICK   CLAYS. 


[BULL.    NO.  9 


Table  5 — Continued. 

S,b-MOBERLY,  MISSOURI, 
Transverse. 


Modulus 

No. 

Breadth, 
inches. 

Depth- 
inches. 

Span- 
inches. 

Load- 
pounds. 

of 
Rupture- 
pounds 
per  sq.  in. 

Av.Mod. 

Var. 
from  av. 

Per  cent 
var. 

1... 

3.24 

3.62 

6 

9930 

2100 

2130 

-30 

1.4 

2.... 

3,24 

3.66 

6 

10900 

2270 

+140 

6.6 

3.... 

3.26 

3.66 

6 

11570 

2310 

+180 

8.4 

4.... 

3.24 

3.40 

6 

7840 

1890 

-240 

11.3 

5.... 

3.24 

3.60 

6 

10910 

2340 

+210 

9.9 

6.... 

3.18 

3.66 

6 

10070 

2130 

0 

0 

7.... 

3.18 

3.62 

6 

10220 

2210 

+80 

3.8 

8.... 

3.30 

3.72 

6 

9470 

1860 

-270 

12.7 

9.... 

3.30 

3.66 

6 

10720 

2180 

+50 

2.3 

10.... 

3.18 

3.66 

6 

11270 

2380 

-250 

11.7 

11.... 

3.30 

3  62 

6 

9480 

1970 

-160 

7.5 

12.... 

3.22 

3.66 

6 
Average 

9120 

1910 

—220 

10.3 

121500 

25550 

85.9 

10125 

21300 

7.2 

Absorption 


Number. 


Kilos. 


Dry. 


Wet. 


Gain, 


Per  cent. 


2 

3 

h.l 


2.59 

2.805 

2.39 

2.66 

2.625 


2.655 
2.875 
2.475 
2.775 
2  71 


.065 
.075 
.085 
.115 
.085 


Av 


2.5 
2.7 


4  3 

3.2 


16.2 


3.2 


R.b-NELSONVILLE,  OHIO. 
Transverse, 


Modulus 

No. 

Breadth- 
inches. 

Depth- 
inches. 

Span- 
inches. 

Load- 
pounds. 

of 
Rupture- 
pounds 
per  sq.  in". 

Av.Mod. 

Var. 
from  av. 

Per  cent 
var. 

! 

3.24 

4.02 

6 

9050 

1560 

1790 

-230 

12.8 

2.... 

3.30 

3.96 

6 

9350 

1630 

—160 

8.9 

3.... 

3.24 

3.96 

6 

10910 

1900 

+110 

6.1 

4... 

3.30 

4.02 

6 

11050 

1870 

+80 

4.5 

5.... 

3.24 

4.02 

6 

11750 

2030 

+240 

*            13.4 

6.... 

3.24 

4.02 

6 

9610 

1680 

-110 

6.1 

7.... 

3.30 

4.08 

6 

10900 

1780 

—10 

0.6 

8.... 

3.24 

3.96 

6 

11820 

2100 

+310 

17.3 

9.... 

3.24 

4.08 

6 

10390 

1800 

+10 

0.6 

10.... 

3.30 

3.96 

6 

9580 

1670 

—120 

6.7 

11.... 

3.24 

4.02 

6 

10860 

1870 

+80 

4  5 

12 ... . 

3.24 

4.08 

6 

Average 

9600 

1600 

-190 

10.6 

124870 

21490 

92.1 

10406 

1790 

7.7 

TALBOTl 


TESTS    OF    PAVING    BRICK. 

Table  5 — Continued. 

Absorption. 


Ill 


Number. 

Kilos. 

Dry. 

Wet. 

Gain. 

Per  cent. 

b,l  .     ..                 

3.465 

3.53 

3.54 

3.66 

3.43 

3  53 
3.58 
3.60 
3.71 
3.485 

.065 
.05 
.06 
.05 

.055 

Av 

1.9 

2 

14 

3 

1.1 

b.,1  

1.3 

2 

1.6 

7.9 

1  6 

Crushing, 


Number. 


Size- 
inches. 


Area- 
square  inches. 


Stress  — 
lb.  per  sq.  in. 


1 

3ii  x  i% 

3%x4 

3^x4i4 

m  x  4:;. 
m x  r_ 

15 

13 

13.8 

14.2 

15 

70500 
64425 
39525 
52450 
39550 

4700 

11 

4950 

10 

2860 

4 

3680 

7 

2640 

18830 

Av 3766 

R2b-PEEBLE'S  BLOCK,  PORTSMOUTH,  O. 
Transverse  Test. 


No. 

Breadth- 
inches. 

Depth- 
inches. 

Span- 
inches. 

Load- 
pounds. 

Modulus 

of 
Rupture- 
pounds 
per  sq.  in. 

Variation 
Av.Mod.        from 
average. 

Per  cent 
variation. 

1  ....             3.22    t           3.90 

2  ....             3.18                3  SO 

6 
6 
6 
6 
6 
6 
6 
6 
6 
6 
6 
6 

Av  .... 

10750 
14420 
12590 
12420 
11980 

1980 
2690 
2270 
2250 
2180 

• 
2.-05              -525 
—185 

21.0 

7.4 

9.4 

10.2 

13.0 

6.6 

9.8 

15.8 

11.0 

21.4 

3  .... 

3.18 
3.22 
3.18 
3.12 
3.18 
3.14 

3.96 
3.94 
3.94 
3.90 
3.90 
3  86 

—235 

4  .... 

—255 

5 

-325 

6  .... 

12300                 2340 
12140                 2260 
15060                 2900 
15290     1            2780 
16490                3040 

—165 

7  .... 

—245 

8  .... 

^-395 

9  .... 

10  .... 

3.18                3.94 
3  12                3.96 

-275 

--535 

11  ....             3.18                3.90 

15850 
13470 

2950 
2410 

—445 

17  8 

12....             3.22                3.98 

-95 

3.8 

162760 

30050 

147.2 

13563 

2505 

12.3 

112 


PAVING    BRICK    AND    PAVING    BRICK   CLAYS. 

Table  5 — Continued. 
R  2b— Absorption. 


[bull.  no.  9 


Kilos. 

Number. 

Dry. 

Wet. 

Gain. 

Per  cent. 

ba 

3.375 

3.52.-) 
3.395 
3.5 
3.46 

3.45 
3.6 

3.47 

3.575 

3.535 

.075 
.075 
.075 
.075 
.075 

Average 

2.2 

2 

2.1 

3 

2  2 

b.,1 

2  1 

2 

2.2 

10.8 

2.2 

J,b-PITTSBURG,  KAN. 
Transverse. 


No. 

Breadth- 
inches. 

Depth- 
inches. 

Span—  I    Load- 
inches.'      pounds. 

Modulus 

of 
Rupture- 
pounds 
per  sq. in. 

Av.Mod. 

Variation 

from 
average. 

Per  cent 
variation. 

1.... 

9 

2. CO 

2.60 
2.50 
2.44 
2.62 
2.55 
2.58 
2.60 
2.45 
2.58 
2.45 
2.52 

3.70 
3.78 
3.80 
3.82 
3.70 
3.80 
3.85 
3.94 
3.86 
3.85 
3.80 
3.92 

6 
6 
6 
6 
6 
6 
6 
6 
6 
6 
6 
6 

Av.... 

9870 

7830 

7860 

11600 

8420 

10390 

10110 

8940 

9960 

7950 

8210 

8120 

2500 
1900 
1960 
2940 
2130 
2530 
2380 
2000 
2160 
1870 
2100 
1890 

2220 

+280 
-320 
-260 
+720 
—  90 
+310 
+160 
-220 
+240 
—350 
—120 
—330 

12.6 
14.4 

3.... 

11.7 

4.   .. 

32.5 

5.... 

4.1 

6.... 

14.0 

7 

7.2 

8.... 

10.0 

9.... 

10.8 

10.... 

15  8 

11.... 

5.4 

12.... 

14.8 

109360 

26660 

153.3 

9130 

2220 

12.8 

Absorption. 


Kilos. 

Number. 

Dry. 

Wet. 

Gain. 

Per  cent. 

bil 

2.318 

2.33 

2.473 

2.30 

2.49 

2.405 
2.37 
2.52 
2.335 

2.55 

.087 

.04 

.047 

.035 

.06 

Average.. 

3.8 

9 

1.7 

3 

1.9 

b2l 

1.5 

9 

2.4 

11.3 

2.3 

TALBOT.] 


TEST   OF    PAVING    BKICK. 

Table  5 — Continued. 
Crushing. 


113 


Number. 

Size- 
inches. 

Area- 
inches. 

Load- 
pounds. 

Stress- 
lbs,  per  sq.  in. 

6 

2^  x  2.% 

2'.-x  2% 
2Y2  x  2-v 
2'ox  3 
2*1x3 

6.22 
6.9 
6.6 
7.5 
7.5 

52000 
78000 
96900 
74500 
57700 

Average 

8400 

6  .... 

11300 

9 

14600 

9 

99  iO 

12 

7700 

51940 

10388 

K9b-POSTON  BLOCK,  CRAWFORDSVILLE,  IND. 

Transverse. 


No. 

Breadth- 
inches. 

Depth- 
inches. 

Span- 
inches. 

Load- 
pounds. 

Modulus 

of 
Rupture- 
pounds 
per  sq.  in. 

Av.Mod. 

Variation 

from 
average. 

Per  cent 
variation. 

1  .... 

2  .... 

3.68 
3.53 
3.75 
3.62 
3.65 
3.60 
3.65 
3.50 
3.65 
3.62 

4.10 

3.95 
4.00 
4.15 
4.02 
4.05 
4.10 
4.02 
3.88 
4.05 

6 

6 
6 
6 
6 
6 
6 
6 
6 
6 

Average 

4000 
6340 
5030 
4390 
3760 
4920 
4120 
4550 
4870 
3960 

585 
1040 
755 
635 
575 
755 
605 
725 
79) 
600 

705 

-120 

+335 
+  50 
-  70 
—130 
+  50 
—100 
+  20 
+  90 
—105 

17.0 
47.5 

3  .... 

7.1 

4  .... 

9.9 

5  .... 

18.4 

6  .... 

7  1 

7  .... 

14.2 

8  .... 

2.8 

9  .... 
10  ... . 

12.8 
14.9 

45910 

7070 

151.7 

4594 

705 

15.2 

. 

Absorption. 


Kilos. 

Number. 

Dry. 

Wet. 

Gain. 

Per  cent. 

"'I:::::::::::::::::::::::::-:::::::: 

2.305 

2.66 

3.132 

2.415 

2.37 

2.564 
2  92 
3.38 
2.68 
2.636 

.259 

.26 

.248 

.265 

.268 

Average 

11.2 
9.8 

3 

7  9 

b2l 

2 

11.0 
11.2 

51.1 

10.2 

-8  G 


114 


PAVING   BRICK   AND    PAVING   BRICK   CLAYS.  tBULL-  N0-  9 

Table  5 — Continued. 
Crushing. 


Number. 

Size 
inches. 

Area 
inches. 

Load- 
pounds. 

Stress- 
lb.  per  sq. in. 

1 

3^x4 

3^x4^ 

3^x4 

3^x4 

14. 5* 

15.4 

16.3 

14.5 

14.5 

56700 
60500 
69700 
50000 
52400 

3900 

4 

5 

3940 

4280 

6 

3950 

7 

3600 

19670 

Average.  3934 

K9c-POSTON  BLOCK,  CRAWFORDSVILLE,  IND. 
Transverse. 


No. 

Breadth- 
inches. 

Depth- 
inches. 

Span- 
inches. 

Load- 
pounds. 

Modulus 

of 
Rupture- 
pounds 
per  sq.  in. 

Av.Mod. 

Variation 

from 
average. 

Per  cent 
variation. 

1 

9 

3.65 
3.55 
3.65 
3.62 
3.55 
3.50 
3.55 
3.55 
3.60 

3.85 
3.80 
3.85 
3.90 
3.90 
3.90 
3.95 
3.98 
3.95 

6 
6 
6 
6 
6 
6 
6 
6 
6 

Av 

7300 
4790 
4960 
5230 
8230 
5470 
10380 
5690 
6490 

58540 

1220 
840 
830 
860 

1380 
930 

1690 
910 

1040 

9700 

1080 

+140 
—240 
-250 
-220 
+300 
—150 
+610 
—170 
-  40 

13.0 
22.2 

3 

23.2 

4 

20.4 

5 

27.8 

6 

7 



13.9 
56.6 

8 

15.7 

9 

3.7 

196.5 

6505 

1080 

21.8 

Absorption. 


Kilos. 

Number. 

Dry. 

Wet. 

Gain. 

Per  cent. 

cxl 

3.555 

3.22 

3.71 

3.34 

3.23 

3.79 

3.444 

3.87 

3.542 

3.478 

.235 

.222 

.16 

.202 

.248 

Average 

6.7 

2 

6.9 

3 

4.3 

c2l 

6.0 

9 

7.7 

31.6 

6.3 

TALBOT.] 


TESTS   OF   PAVING   BRICK. 

Table  5—  Continued. 
Crushing. 


115 


Number. 

Size- 
inches. 

Area- 
square  inches. 

Load- 
pounds. 

Stress 
lb.  per  sq.  in. 

4 

3V4  x3 
S%  x  VA 
3%  x  3 
35sx3 
*%  x  3 

97.7 
11.8 
10.9 
10.9 
10.9 

86400 
114200 

74300 
100400 

78800 

8900 

5 

9700 

8 

6800 

9 

9200 

9 

7230 

41830 

Average  ..8366 

K9d-POSTON  BLOCK,  CRAWFORDSVILLE,  IND. 

Transverse. 


No. 

Breadth- 
inches. 

Depth- 
inches. 

Span- 
inches. 

Load- 
pounds. 

Modulus 

of 
Rupture- 
pounds 
per  sq.  in. 

Av.Mod. 

Var. 
from  av. 

Per  cent, 
var. 

1  .. 

3.60 
3.50 
3.48 
3.48 
3.50 
3.60 
3.50 
3.50 
3.55 
3.62 

3.82 

3.85 
3.88 
3.95 
3.92 
3.70 
3.90 
4.00 
3.90 
3.90 

6 
6 
6 
6 
6 
6 
6 
6 
6 
6 

Average 

9700 
10560 
15020 
12460 
10010 
11640 
13510 
14420 
12450 
11450 

1660 
1830 
2580 
2070 
1680 
2140 
2280 
2320 
2070 
1880 

2050 

-390 
-220 
+530 
+  20 
-370 
+  90 
+230 
+270 
+  20 
-170 

19.0 
10.7 

3 

25.8 

4 

1.0 

5  .. 

18.0 

6 

4.4 

7 

11.2 

8 

13.2 

9  .. 
10  .. 

1.0 

8.3 

121220 

20510 

112.6 

12120 

2050 

11  3 

Absorption. 


Number. 

Kilos. 

Per  cent 

Dry. 

Wet. 

Gain. 

da 

3.38 
3.51 
3  70 
3.675 
3.82 

3.482 

3.622 

3.79 

3.76 

3.872 

.102 

.112 

.09 

.085 

.052 

Average''.. 

3  0 

2 

3  2 

3 

2.4 
2  3 

d2l 

2 :..::::..::..:::::::::::::::: 

1  4 

12.3 

2.5 

H6 


PAVING   BRICK   AND    PAVING   BRICK   CLAYS. 

Table  5 — Continued. 
Crushing. 


[bull.  no.  9 


Number. 


2 
5 
9 

10 


Size- 
inches. 


3^x33^ 
33^x2% 
3^x2^ 
3^x2% 
3^x2^ 


Area- 
square  inches. 


12.2 
9.6 
8.7 


Load- 
pounds. 


97800 
97800 
79200 
95000 
101200 


Stress- 
lbs,  per sq. inch. 


8020 
10200 
9100 
9900 
11600 


48820 


Average 


.9764 


K9e-POSTON  BLOCK.  CRAWFORDSVILLE,  IND. 
Transverse. 


No. 

Breadth, 
inches. 

Depth - 
inches. 

Span- 
inches. 

Load- 
pounds. 

Modulus 

of 
Rupture, 
pounds 
per.sq.in 

Av.Mod. 

Var. 
from  av. 

Per  cent 
var. 

Remarks. 

1 

2 

3.50 
3.67 
3.60 
3.55 
3.55 
3.55 

3.66 
3.55 
3.30 
3.68 
3.80 
3.60 

6 
6 
6 
6 
6 
6 

Average 

13100 
11 100 
10970 
5420 
11790 
10120 

2520 
2170 
2520 
1020 
2070 
1980 

2050 

+470 

+120 

+470 

—1030 

+20 

-70 

22.9 

5.8 

22.9 

50.2 

1.0 

3.4 

Badly 

ov'rburn'd 

and 

very 

irregular 

3 

4 

5 

6 

62500 

12280 

106.2 

10120 

2050 

17.7 

Absorption. 


Number. 

Kilos. 

Dry. 

Wet. 

Gain. 

Per  cent. 

■I"::::::::'::::::;::::::::: 

3.255 
3.41 

3.485 
3.465 
3.665 

3.285 

3.433 

3.505 

3.50 

3.69 

.03 

.023 

.02 

.035 

.025 

Average 

0.9 

.7 

.6 

1.0 

.7 

3 

e2l 

2 

3.9 

0.8 

Crushing. 


Number. 

Size- 
inches. 

Area- 
square  inches. 

Load- 
pounds. 

Stress- 
lb.  per  sq. in. 

1 

m  x  2% 

3^x2^ 
3^x3 
PA  x  2H 
3^x2% 

9.6 
8.7 
10.5 
7.8 
9.6 

108400 
89500 

134000 
80500 
66000 

Average 

11300 
10300 
12800 
10300 
6900 

2 

3 

4 

4.... 

15600 

10320 

TALBOT] 


TESTS   OF    PAVING    BRICK. 

Table  5 — Continued. 

KGb-PURINGTON  BLOCK. 
Absorption. 


117 


Number. 

Kilos. 

Percent. 

Dry. 

Wet. 

Gain. 

1 

6.53 

2 

5.37 

3 

5.48 

4 

5  82 

5 

8  07 

Average 

31.27 

6.25 

Knc. 


cl 

3.75 

2 



3.76 

cl 

4.92 

9 

4.92 

3 

4.38 

Average 

19.97 

3.99 

K„d. 


dl  

0.27 

9 

0.84 

dl 

0.28 

2 

0.57 

3  

0.00 

Average 

1.96 

0  39 

KBe. 


el 

1.25 

2 

0.43 

3 

0.95 

4 

0.98 

5 

0.85 

Average  .... 

4.46 

0.89 

KBb, 


III  

6.48 

2...                 

7.55 

Ill 

5.88 

2 

4.90 

3 

7.76 

Average 

32.57 

6.51 

118 


PAVING    BRICK   AND    PAVING   BRICK   CLAYS. 

Table  5 — Continued. 

Pitrington  Block— Concluded. 
K6c2. 


[BULL.    NO.    9 


Number. 

Kilos. 

Percent. 

Dry. 

Wet. 

Gain. 

cll2l 

4  33 

9 

7  17 

oil   1 

4  74 

2 

3  68 

3 

8  29 

Average 

28.21 

5.64 

K4b-SPRINGFIELD,  ILL. 
Transverse. 


No. 

Breadth, 

inches. 

Depth- 
inches. 

Span- 
inches. 

Load- 
pounds. 

Modulus 

of 
Rupture, 
pounds 
persq.in. 

Av.Mod. 

Variation 

from 
average. 

Per  cent 
variation . 

1  .... 

2  .. 

2.73 
2.75 
2.75 
2.70 
2.72 
2.72 
2.70 
2.70 
2.72 
2.70 

4.20 
4.22 
4.10 
4.15 
4.20 
4.15 
4.15 
4.10 
4.10 
4.18 

6 
6 
6 
6 
6 
6 
6 
6 
6 
6 

Average 

4150 
5120 

3340 
3860 
5010 
6150 
6170 
5380 
5160 
6620 

50990 

780 

945 

650 

750 

950 

1180 

1195 

10.0 

1020 

1260 

980 

-200 

-  35 
-330 
-230 

-  30 
+200 
+215 
+  90 
+  40 
+280 

20.4 
3.6 

3  . 

33.7 

4 

23.5 

5  .... 

3.1 

6  .. 

20.4 

7  .. 

21.9 

8 

9.2 

9    . 

4.1 

10 

28.6 

9800 

168.5 

5100 

980 

16.8 

Absorption. 


Kilos. 

Per  cent. 

Number. 

Dry. 

Wet. 

Gain. 

1 

1.415 

1.625 
1.93 
1.93 
1.86 

1.595 
1.825 
2.155 
2.165 

2.085 

.180 

.2 

.225 

.235 

.225 

Average 

12.7 

2           

12.3 

3 

11.7 

4 

12.2 

5 

12.1 

61.0 

12.2 

TALBOT.] 


TESTS   OF    PAVING   BRICK. 

Table  5— Continued. 
Crushing. 


119 


Number. 

Size- 
inches. 

Area- 
square  inches. 

Load- 
pounds. 

Stress- 
lb.  per  sq. in. 

2 

2^x3^ 
2%  x  394 
2%  x  314 
2%x3 
294x4 

8.9 

10.3 

8.9 

8.2 

11.0 

10200 
15700 
19100 
23200 
28800 

1150 

1520 

6 

2150 

6 

2840 

9 

2620 

10280 

Average  ..2056 

K4c-SPRINGFIELD,  ILL. 

Transverse. 


No. 

Breadth- 
inches. 

Depth- 
inches. 

Span- 
inches. 

Load- 
pounds. 

Modulus 
of 

Rupture- 
pounds 

per  sq. in. 

Av.Mod. 

Variation 

from 
average. 

Per  cent 
variation. 

1 

2 

2.58 
2.65 
2.60 
2.55 
2.62 
2.62 

3.95 

3.80 
3.85 
3.90 
4.00 
3.95 

6 
6 
6 
6 
6 
6 

Average 

11220 
10350 
12630 

8260 
10510 

9400 

2520 
2440 
2960 
1920 
2260 
2080 

2360 

+160 

+  80 
+600 
—410 
—100 
—320 

6.8 
3.4 

3 

•  25.4 

4 

18.7 

5 

4.2 

6 

13.6 

62370 

14180 

72.1 

10395 

2360 

8.0 

Absorption. 


Kilos. 

Per  cent. 

Number. 

Dry. 

Wet. 

Gain. 

l „ 

2 

2.52 

2.51 

2.54 

2.425 

2.54 

2.67 
2.61 
2.67 
2.56 
2.645 

.15 

.10 

.13 

.135 

.105 

A  verage 

5.95 
4.00 

3 

4 

5.12 

5.57 

4.14 

24.78 

5.00 

120 


PAVING   BRICK    AND    PAVING    BRICK   CLAYS, 

Table  5— Continued. 

Crushing. 


[bull.  no.  9 


Number. 

Size- 
inches. 

Area- 
square  inches. 

Load- 
pounds. 

Stress- 
lb.  per sq. in. 

1 

2^x4 

2r>8  x  m 
%  xm 

2%xM 

10.5 
9.8 
9.2 
9.8 

8.5 

55400 
52000 
56700 
40200 
41700 

Average 

■ 

5 

5280 

5300 

6 

6170 

6 

4100 

4900 

25750 

5150 

K4d-SPRINGFIELD.  ILL 
Transverse. 


No. 

Breadth- 
inches. 

Depth- 
inches. 

Span- 
inches. 

Load- 
pounds. 

Modulus 
of 

Rupture- 
pounds  • 

per  sq.  in. 

Av.Mod. 

Variation 

from 
average. 

Per  cent 
variation. 

1  .... 

2.68 
2.62 
2.58 
2.60 
2.62 
2.62 
2.62 
2.65 
2.65 
2.68 
2.55 
2.65 

2.65 
3.85 
3.88 
3.80 
3.82 
3.78 
3.90 
3.70 
3.70 
3.70 
3.90 
3.80 

6 
6 
6 
6 
6 
6 
6 
6 
6 
6 
6 
6 

Average 

9120 
10770 
11290 

8350 
10690 

7470 
10290 

7850 
11360 

8170 

8350 

9410 

2300 
2490 
2610 
2000 
2520 
1800 
2330 
1950 
2820 
2010 
1940 
2220 

2250 

+  50 
+240 
+360 
—250 
+270 
—450 
+  80 
—300 
+570 
—240 
—310 
—  30 

2.2 
10  7 
16.0 
11.1 
12  0 

3  .... 

4  .... 

5  .... 

b  .... 

20  0 

7  .... 

3  6 

8  .... 

13  3 

9  .... 

25  3 

10  .... 

10  7 

11  .... 

13  8 

12  .... 

1  3 

113120 

26990 

140.0 

9430 

2250 

11  7 

Absorption. 


Number. 

Kilos. 

• 

Dry. 

Wet. 

Gain. 

Per  cent. 

dx1 

2.69 

2.76 

2.645 

2.79 

2.565 

2.72 

2.794 

2.675 

2.82 

2.593 

.03 

.034 

.03 

.03 

.028 

Average 

1.1 
1.2 
1.1 
1.1 
1.1 

2 

Dol 

2 

3 

5.6 

1.1 

TALBOTj 


TESTS   OF    PAVING    BRICK. 

Table  5 — Continued. 

K4e-SPRINGFIELD,   ILL. 
Transverse  Test. 


121 


No. 

Breadth- 
inches. 

Depth- 
inches. 

Span- 
inches. 

Load- 
pounds. 

Modulus 

of 
Rupture- 
pounds 
persq.in. 

Av.Mod. 

Variation 

from 
average. 

Per  cent 
variation. 

1.... 
2 

2.60 
2.63 
2.65 
2.70 
2.70 
2.63 

3.98 
4.03 
4.10 
4.08 
4.05 
4.10 

6 
6 
6 
6 
6 
6 

Average 

16150 
3000 
9140 
3800 

12260 
4430 

3530 
635 
2000 
1760 
2490 
905 

1890 

+1640 
—1255 
+  110 

—  130 

+  600 

—  985 

86.7 
66.4 

3 

5.8 

4 

6.9 

5 

31.8 

6.... 

52.2 

53780 

11320 

249.8 

8960 

1890 

41  6 

Absorption. 


Kilos. 

Number. 

Dry. 

Wet. 

Gain. 

Per  cent. 

1 

9 

1.69 

1.625 

1.64 

2.37 

2.635 

1.702 
1.642 
1.655 
2.392 
2.665 

.012 
.017 
.015 
.022 
.030 

Average 

0.6 

.7 

3    

.6 

4 

.5 

5 

.5 

2.9 

0.6 

Crushing. 


Number. 

Size- 
inches. 

Area- 
square  inches. 

Load- 
pounds. 

Stress- 
lb.  per  sq.  in. 

1 

2%  x  'S% 
2%  x  4 
2%  x  4 
2^x2M 
2^x3 

8.8 

10.5 

10.5 

7.2 

7.9 

33200 
31800 
31600 
34600 
26300 

Average 

3780 

3 

3020 

3 

3000 

4 

4800 

6...    . 

3340 

17940 

3588 

122 


PAVING   BRICK   AND    PAVING   BRICK   CLAYS. 

Table  5 — Continued. 

V8C-STREATOR  PAVING  BRICK  COMPANY. 
Absorption. 


[BULL.    NO.    9 


Number. 

Kilos. 

Per  cent. 

Dry. 

Wet. 

Gain. 

Col 

0  89 

2 

3  96 

c  1 

5  05 

2 

4  24 

3  ..                                       

3  41 

Average 

17.55 

3.51 

V8d. 


d  1    

0.47 

2     .                                       

0  50 

d2l 

0.46 

2 

0.48 

3...    

0.46 

Average 

2.37 

.49 

V8e. 


e„i                              

0.00 

"2 

0.50 

el 

0.47 

2 

0.49 

3                           

0.50 

Average 

1.96 

.39 

Ki;jb-TERRE   HAUTE  BLOCK,   TERRE   HAUTE,   IND. 
Transverse. 


No. 

Breadth- 
inches. 

Depth- 
inches. 

Span- 
inches. 

Load- 
pounds. 

Modulus 

of 
rupture,— 

pounds 
persq.  in. 

Av.Mod. 

Var. 
from  av. 

Per  cent 
var. 

1 

2. 

3.40 
3.20 
3.35 
3.25 
3.25 
3.22 
3.35 
3.42 
3.25 

4.00 
4.10 
4.05 
3.95 
3.98 
3.90 
3.95 
4.10 
3.90 

6 
6 
6 
6 
6 
6 
6 
6 
6 

Average 

8510 
7960 
8560 
9170 
8030 
4480 
8520 
12060 
5560 

1410 
1330 
1410 
1630 
1410 
825 
1470 
1890 
1010 

1375 

+  35 
—  45 
+  35 
+255 
+  35 
-550 
+  95 
+515 
-365 

2.5 
3.3 

3 

2.5 

4  . 

18.6 

5 

2.5 

6  . 

40.0 

7 

6.9 

8 

37.5 

9 

21.6 

72850 

12385 

135.4 

8090 

1375 

15.0 

TALBOT.] 


TESTS   OF    PAVING    BRICK. 

Table  5 — Continued. 
Absorption. 


123 


Kilos. 

Number. 

Dry. 

Wet. 

Gain. 

Per  cent. 

b,l    

2.69 

2.758 

2.39 

2.42 

2.625 

2.948 

3.04 

2.565 

2.64 

2.872 

.258 

.282 

.175 

.22 

.247 

Average 

9.6 

1 .::::.:...:..: 

3  

10.2 
7.3 

b,l  

9.1 

g 

9.4 

45.6 

9.1 

K10c-TERRE  HAUTE  BLOCK,   TERRA  HAUTE,   IND. 
Transverse, 


No. 

Breadth- 
inches. 

Depth- 
inches. 

Span- 
inches. 

Load- 
pounds. 

Modulus 

of 
rupture,— 

pounds 
per  sq.  in. 

Av.Mod. 

Var. 
from  av. 

Per  cent 
var. 

1 

2 

3.15 
3.30 
*     3.30 
3.25 
3.22 
3.30 
3.20. 
3.20 
3.22 
3.35 

3.71 
3.72 
3.65 
3.80 
3.88 
3.75 
3.80 
3.80 
3.94 
3.85 

6 
6 
6 
6 
6 
6 
6 
6 
6 
6 

Average 

11100 

4330 

11730 

4750 

10560 

12160 

8540 

10360 

14480 

11660 

2300 
855 

2410 
910 

1910 

+  390 
—1055 

-  500 
-1000 

-  50 
+  450 

-  250 
+    40 
+  690 

-  200 

20.4 

3 

26.2 

4 

52.4 

5 

1960 
2360 
1660 
1950 
2600 
2110 

2.6 

6 

23.5 

7 

13.1 

8 

2.1 

9. 

36.1 

10 

10.5 

99670 

19110 

242.1 

9667 

1910 

24.2 

Absorption. 


Number, 


Kilos. 


Do- 


Wet. 


Gain. 


Per  cent. 


c.l 

2.865 

3.33 

2.615 

2.91 

3.065 

2.97 

3.37 

2.658 

2.968 

3.105 

.105 

.04 
.043 
.058 
.04 

Average 

3.7 
1.2 

3 

1.6 

cl 

2.0 

2 

1  3 

9.8 

2.0 

124 


PAVING    BRICK   AND    PAVING   BRICK   CLAYS.  [bull.  no.  9 

Table  5 — Continued. 

Klfld-TERRE  HAUTE  BLOCK,  TERRE  HAUTE,  IND. 

Transverse. 


No. 

Breadth, 
inches. 

Depth- 
inches. 

Span- 
inches. 

Load- 
pounds. 

Modulus 

of 

Rupture, 

pounds 

persq.in. 

Av.Mod. 

Var. 
from  av. 

Percent 
var. 

1 

3.20 
3.25 
3.15 
3.20 
3.20 
3.23 
3.20 

3.75 
3.75 
3.75 
3.90 
3.80 
3.88 
3.85 

6 
6 
6 
6 
6 
6 
6 

Average 

14300 
11680 
13300 
9680 
11280 
12290 
11730 

2870 
2300 
2710 
1800 
2210 
2290 
2230 

2340 

+530 

-  40 
+370 
-540 
—130 

-  50 
-110 

22  6 

2... 

1  7 

3... 

15  8 

4 

23.1 

5 

5.5 

6 

2.1 

7... 

4  7 

84260 

16410 

75.5 

12040 

2340 

10.8 

Absorption. 


Kilos. 

Number. 

Dry. 

Wet. 

Gain. 

Per  cent. 

d,l  

2.843 

2.61 

2.69 

2.68 

2.51 

2.868 
2.625 
2.718 
2.718 
2.538 

.025 
.015 
.028 
.038 
.028    • 

Average 

0  9 

2  I:::::::::::::::::::::::::::::::: 

0.6 

3 

1.0 

d2l  

1.4 

2  

1.1 

5.0 

1.0 

Crushing. 


Number. 

Size- 
inches. 

Area- 
square  inches. 

Load- 
pounds. 

Stress- 
lbs,  per  sq 

in. 

2 

3M  x  Z\i 

3^x4 

3Mx3 

3M  x  zyz 

10.6 
13. 
9.7 
11.4 
10.1 

76700 
76800 
34700 
71500 
70000 

Average 

7250 

4.... 

5900 

4 

3580 

5 

6250 

6 

6940 

29920 

5984 

TALBOT.] 


TESTS   OF    PAVING    BRICK. 


125 


Table  5— Continued. 


KlOe 


TERRE  HAUTE  BLOCK,  TERRE  HAUTE,   IND. 

Transverse. 


No. 

Breadth- 
inches. 

Depth- 
inches. 

Span  - 
inches. 

Load- 
pounds. 

Modulus 

of 
Rupture- 
pounds 
per  sq.  in. 

Av.Mod. 

Variation 

from 
average. 

Per  cent 
variation. 

1  .. 

3.25 
3.33 
3.45 
3.40 
3.25 
3.32 
3  30 
3.30 
3.35 

4.00 
3.88 
4.15 
4.10 
3.85 
4.22 
4.00 
4.00 
3.85 

6 
6 
6 
6 
6 
6 
6 
6 
6 

Average 

18010 
12260 

7250 
13200 

8020 
10020 
10100 

7930 
12670 

3130 
2200 
1100 
2080 
1500 
1530 
1720 
1350 
2290 

1880 

+1250 
+320 
—780 
+200 
—380 
—350 
—160 
-530 
+410 

66.5 
17.0 

3 

41.5 

4 

10.6 

5 

20.2 

6 

18.6 

7  .. 

8.5 

8 

28.2 

9 

21.8 

99460 

16900 

232.9 

11050 

1880 

25.9 

Absorption. 


Kilos. 

Number. 

Dry. 

I 
Wet.        | 

1 

Gain. 

Per  cent. 

dl  

2.74 
3.03 
2.80 
2.74 

2.578 

2.765 

3.048 

2.82 

2.762 

2.605 

.025 

.018 

.02 

.022 

.027 

Average 

0.9 

2  

.6 

3  . 

.7 

c,l  

.8 

2  

1.0 

4.0 

0.8 

Crushing. 


Number. 

Size- 
inches. 

Area- 
square  inches. 

Load- 
pounds. 

Stress- 
lb.  per  sq.  in. 

7 

8 

3*4  x  3% 

3*4x4*6     . 

3*4x31^ 

3Mx4% 

ii. 

12.2 
13.4 
11.4 
14.2 

24300 
43000 
21000 
21400 
41500 

Average 

2200 
3590 

9 

1570 

9 

1880 

10.... 

2990 

12090 

2418 

126 


H2b 


PAVING    BRICK   AND    PAVING   BRICK   CLAYS. 

Table  5— Continued. 

TOPEKA,  KAN. 

Transverse. 


[bull.  NO. 


No. 

Breadth- 
inches. 

Depth- 
inches. 

Span- 
inches. 

Load- 
pounds. 

Modulus 

of 
Rupture- 
pounds 
per  sq.  in. 

Av.Mod. 

Variation 

from 
average. 

Per  cent 
variation. 

2  .... 

3  .... 

2.58 
2.34 
2.46 
2.46 
2.52 
2.46 
2.28 
2.44 
2.46 
2.52 
2.46 
2.44 

• 

3.90 
3.84 
3.90 
3.88 
3.84 
4.02 
4.02 
3.90 
3.96 
3.84 
3.96 
3.90 

6 

6 
6 
6 
6 
6 
6 
6 
6 
6 
6 
6 

Average 

8840 

10540 

12610 

10360 

8280 

11250 

10160 

8950 

9740 

9090 

9500 

5520 

2030 
2750 
3040 
2520 
2020 
2550 
2480 
2180 
2270 
2220 
2220 
1340 

2300 

-  270 
+  450 
+  740 
+  220 

-  280 
+  250 
+  180 

-  120 

-  30 

-  80 

-  80 

-  960 

11.7 
19.6 

4  .... 

32.2 

5  .... 

9  6 

6  .... 

12  2 

7    . 

10  9 

8 

7  8 

9  .... 

5.2 

10  .... 

1.3 

11  .. 

3.5 

12  .... 

3.5 

13  .... 

41.8 

114840 

27620 

159.3 

9570 

2300 

13.3 

Absorption. 


Kilos. 

Number. 

Dry. 

Wet. 

Gain. 

Per  cent. 

bxl  

2.235 
2.19 

2.098 
2.092 
2.182 

2.315 
2.225 
2.118 
2.115 
2.215 

.02 

.035 

.02 

.023 

.033 

Average 

0.9 

2  

1.6 

3  

1.0 

b2l  

1.0 

2  

1.5 

6.0 

1.2 

K8b-W ABASH  CLAY  CO.,  WEEDERSBURG,  IND. 

Transverse. 


No. 

Breadth- 
inches. 

Depth- 
inches. 

Span- 
inches. 

Load- 
pounds. 

Modulus 

of 
Rupture- 
pounds 
persq.in. 

Av.Mod. 

Variation 

from 
average. 

Per  cent 
variation . 

1  .... 
2 

3.62 
3.60 
3.50 
3.50 
-    3.60 
3.55 
3.60 
3.50 

3.90 
3.95 
4.05 
4.05 
3.90 
4.00 
3.95 
4.09 

6 
6 
6 
6 
6 
6 
6 
6 

Average 

1730 
4170 
4380 
4860 
4530 
2740 
3260 
3630 

285 
670 
690 
765 
745 
435 
520 
585 

585 

—300 
-I-  85 
+105 
+180 
+160 
—150 
+  65 
0 

51.3 
14.5 

3 

17.9 

4 

30.8 

5 

27.3 

6 

25.6 

7 

11.1 

8 

.0 

29300 

4695 

178.5 

3660 

585 

22.3 

TALBOT.] 


TESTS   OF    PAVING   BRICK. 

Table  5 — Continued. 
Absorption. 


127 


Kilos. 

Number. 

Dry. 

Wet. 

Gain. 

Per  cent. 

b.l 

3.128 
3.055 
3.135 
2.712 
3.192 

3.43 

3.338 
3.47 
2.98 
3.485 

.302 
.283 
.335 
.268 
.293 

Average 

9.7 

2 

9.3 

3 

10.7 

b2l 

9.9 

9 

9.7 

49.3 

9.9 

Crushing. 


Number. 

Size- 
square  inches. 

Area- 
square  inches. 

Load- 
pounds. 

Stress- 
lb.  per  sq. in. 

t 

3^x3% 
3^x3  % 
3V2  x  4 

&a  x  m 
sy2xm 

12.7 

12.7 

14. 

10.9 

14.9 

56900 
34300 
26500 
27000 
31800 

4500 

3 

2700 

4 

1890 

4  

2480 

8 

2140 

13710 

Average 2742 

K8c-WABASH  CLAY  CO.,  VEEDERSBURG,  IND. 
Transverse. 


No. 

Breadth- 
inches. 

Depth- 
inches. 

Span- 
inches. 

Load- 
pounds. 

Modluus 
of 

Rupture- 
pounds 

per  sq.  in. 

Av.Mod. 

Variations 

from 
Average. 

Per  cent 
Variation. 

1 

2 

3.50 
3.50 
3.50 
3.52 
3.50 
3.50 
3.55 

3.90 
3.95 
3.90 
3.88 
3.90 
3.98 
3.92 

6 
6 
6 
6 
6 
6 
6 

Average 

5530 
6730 
5120 
7620 
4470 
6010 
7810 

940 
1110 

870 
1300 

755 

980 
1290 

1035 

-  95 
+  75 
—165 
+265 
-280 

-  55 
+255 

9.2 

7.2 

3 

16.0 

4 

25.6 

5 

27.1 

6 

5.3 

7 

24.7 

43320 

7245 

115.1 

6190 

1035 

16  4 

128 


PAVING   BRICK   AND    PAVING   BRICK   CLAYS. 

Table  5 — Continued. 
Absorption. 


[bull.  no.  9 


Number. 


c,l 
2 

3 

Col 

2 


Kilos. 

Dry. 

Wet. 

Gain. 

Percent. 

3.135 
3.130 
3  098 
3.085 
3.202 

3.38 

3.34 

3.375 

3.345 

3.444 

.245 

.21 

.277 

.26 

.242 

Average  

7.8 
6.7 
8.9 
8.4 
7.6 

39.4 

7.9 

Crushing 


Number. 

Size- 
inches. 

Area- 
square  inches. 

Load- 
pounds. 

Stress- 
lbs,  per  sq.  in. 

1 

334  x  4% 
334x4 
334x5 
334x434 
334  x  434 
334  x  2% 
334  x  m 
334x4% 
334  x4M 

15.3 
14.0 
17.5 
15.7 
15.7 
9.2 
16.2 
15.3 
14.8 

83200 
61400 
65900 
47500 
107400 
37200 
72040 
46500 
64400 

Average 

2 

5440 

2 

4380 

3 

3760 

4 

3020 

5 

6800 

6 

4040 

7 

4450 

7 

3040 

4320 

39250 

4361 

K8d-WABASH  CLAY  CO.,  VEEDERSBURG,  IND. 
Transverse. 


No. 

Breadth- 
inches. 

Depth- 
inches. 

Span- 
inches. 

Load- 
pounds. 

Modulus 
of 

Rupture- 
pounds 

per  sq.  in. 

Av.Mod. 

Variation 

from 
average. 

Per  cent 
variation. 

1 

2 

3.48 
3.38 
3.35 
3.45 
3.40 
3.35 
3.40 
3.40 
3.40 

3.80 
3.90 
3.90 
3.80 
3.85 
3.88 
3.80 
3.80 
3.83 

6 
6 
6 
6 
6 
6 
6 
6 
6 

Average 

10350 
5760 
10960 
10990 
7750 
7190 
3110 
9060 
7050 

1860 
1010 
1940 
1990 
1390 
1290 
570 
1660 
1280 

1440 

+420 
—430 
+500 
+550 
—  50 
—150 
—870 
+220 
-160 

29.2 
29  8 

3 

34  7 

4 

38  2 

o 

3  5 

6 

10  4 

7 

60  3 

8 

15  3 

9 

11  1 

72220 

12990 

232.5 

8020 

1440 

25  8 

TALBOT] 


TESTS   OF    PAVING   BRICK. 

Table  5 — Continued. 


129 


Absorption. 


Kilos. 

Number. 

Dry 

Wet. 

Gain. 

Per  cent. 

d1 

3  285 

3.22 

3.312 

3.362 

3.362 

3.40 

3.355 

3.445 

3.488 

3.40 

.115 
.135 
.133 
.126 
.138 

3.5 

2 

4.2 

3 

4.0 

dxl 

3.8 

2 : :: 

4.2 

19.7 

Crushing. 


Number. 

Size- 
inches. 

Area- 
square  inches. 

Load- 
pounds. 

Stress- 
lb.  per  sq. 

in. 

1 

3^x3M 
33^x3% 
33^x3 

zy2  x  m 

&A  x3M 

11.4 
12.7 
10.7 
11.4 
11.4 

57800 
35900 
26100 
61500 
71000 

• 

5060 

2 

2820 

5 

2480 

7 

5400 

8 

6230 

21990 

Average  . 

. .  4398 

K8e— WABASH  CLAY  CO.,   VEEDERSBURG,  IND. 
Transverse  Test. 


No. 

Breadth- 
inches. 

Depth- 
inches. 

Span- 
inches. 

Load- 
pounds. 

Modulus 

of 
Rupture- 
pounds 
persq.  in. 

Av.Mod. 

Variation 

from 
average . 

Per  cent 
variation . 

1  .... 

2  .... 

3.50 
3.50 
3.50 
3.50 
3.50 
3.55 
3.50 
3.50 
3.52 
3.52 

3.84 
4.00 
3.95 
4.00 
3.90 
3.80 
3.80 
3.90 
4.00 
4.00 

6 
6 
6 
6 
6 
6 
6 
6 
6 
6 

Average 

4350 
6590 
4050 
4900 
2200 
2700 
1880 
1900 
11000 
9750 

760 
1060 
670 
790 
370 
475 
335 
320 
1760 
1560 

810 

—  50 
+250 
—140 

—  20 
—440 
-335 
-475 
-490 
+950 
+750 

6.2 
30.8 

3  .... 

17.3 

4  .... 

2.5 

5  .... 

54.3 

6  .... 

41.3 

7  .... 

58.6 

8  .... 

60.5 

9  .... 

117.4 

10  ... . 

92.5 

49320 

8090 

481.4 

4930 

810 

48.1 

■9  G 


130 


PAVING   BRICK   AND    PAVING   BRICK   CLAYS. 

Table  5 — Continued. 


[BULL.   NO.  9 


Absorption. 


Number. 

Kilos. 

Dry. 

Wet. 

Gain. 

Per  cent. 

2.11 

2.725 
3.76 
2.495 
3.6 

2.13 

2.77 
3.815 
2.54 
3.67 

.02 

.045 

.055 

.045 

.07 

Average 

1  0 

2 

1  6 

3 

1  5 

4 

1  8 

5 

1  9 

7.8 

1.6 

Crushing. 


Number. 

Size- 
inches. 

Area- 
square  inches. 

Load- 
pounds. 

Stress- 
lb.  persq.  in. 

« 

1 

2 

334x334 
334x3 

33^x33^ 
334  x  334 
334x3% 

12.2 
10.5 
10.9 
12.2 
13.1 

89300 
70600 
100000 
115000 
70100 

7300 
6730 

5 

9160 

'7... 

9450 

10 ".. 

5350 

37990 

Average 7598 

K14b-WESTERN  PAVER,  DANVILLE,  ILL, 
Transverse. 


No. 

Breadth - 
inches. 

Depth- 
inches. 

Span- 
inches. 

Load- 
pounds. 

Modulus 

of 

Rupture, 

pounds 

persq.in. 

Av.Mod. 

Var. 

from  av. 

Per  cent 
var. 

Remarks 

1.... 
2 

3.48 
3.54 
3.48 
3.58 
3.46 
3.60 
3.48 
3.48 
3.46 
3.60 
3.42 
3.58 

4.08 
4.06 
4.02 
3.96 
4.08 
4.02 
4.02 
3.96 
4.02 
3.90 
4.02 
4.02 

6 
6 
6 
6 
6 
6 
6 
6 
6 
6 
6 
6 

Average 

9180 

9820 

11220 

9610 

9260 

10510 

10330 

10310 

10120 

8300 

12860 

10370 

1424 
1515 
1795 
1541 
1447 
1625 
1653 
1'iOO 
1629 
1364 
2094 
1613 

1617 

-193 
—102 

+178 

—  76 
—170 
+     8 
+  36 
+  83 
+  12 
-253 
+477 

—  4 

11.9 
6.3 

11.0 
4.7 

10.5 
0.5 
2.2 
5.1 
0.7 

15.6 

29.5 
0.2 

3... 

4... 

5.... 

6... 

7.... 

8  .. 

9... 

10... 

Irregular 

11.... 

shape 

12... 

caused 

eccentric 
load. 

121890 

19400 

98.2 

10160 

1167 

8.2 

TALBOT] 


TESTS   OF    PAVING    RRICK, 

Table  5— Concluded. 
Absorption. 


131 


Kilos. 

Number. 

Dry. 

Wet, 

Gain. 

Per  cent. 

bjl  

3.512 
3.810 
3.725 
3.505 
3.700 

3.676 
3.975 
3.875 
3.675 
3.855 

.164 
.165 
.150 
.170 
.155 

Average 

4.7 

0 

4.3 

1 

4.0 

bol  

3.9 

-2 .:::::: :..:..:::::::::::::: 

4.2 

21.1 

4.2 

Crushing. 


Number. 

Size- 
inches. 

Area- 
square  inches. 

Load- 
pounds. 

Stress- 
lb.  per  sq. in. 

5 

3^x4 

3^x4 
3^x3% 
3^x3^ 
3^x3^ 

14. 

14. 

13.1 

12.2 

12.2 

50000 
94500 
86800 
51200 
60400 

Average 

3580 
6750 

9 

10 

6640 
4200 

li 

4950 

26120 

5224 

QUALITIES  OF  CLAYS   SUITABLE    FOR    MAKING    PAVING 

BRICK. 

[By  Ross  C.  Puedy.] 


Introduction. 

Nature  of  the  Problems  .Involved — In  Holland  brick  has  been  used  for 
street  paving  for  more  than  a  century,  and  in  the  United  States  for  over 
thirty  years.  During  this  period,  ceramics,  or  the  study  of  clay  working, 
has  been  developed  as  a  science  to  such  an  extent  as  to  become,  especially 
in  the  last  decade,  a  prominent  factor  in  the  technical  advance  that  has 
been  made  in  the  various  clay  industries.  The  application  of  pure  sci- 
ence, notably  physics  and  chemistry,  has  solved  a  great  many  practical 
problems  that  clay  workers  have  met  in  their  endeavor  to  keep  pace 
with  the  ever  increasing  requirements  for  better  quality  and  greater 
adaptations  of  ware. 

Ceramics,  or  the  application  of  pure  science  to  clay  working,  has  been 
developed  chiefly  along  two  lines:  first,  the  applications  of  mechanics 
to  the  evolution  of  methods  of  winning  raw  materials,  and  manufactur- 
ing of  wares;  second,  the  application  of  physical  and  chemical  prin- 
ciples to  the  selection  and  mixing  of  clays  and  minerals. 

Along  these  two  lines  ceramics  has  attained  its  greatest  development 
in  the  pottery,  floor  and  wall  tile,  and  kindred  industries  where  white 
burning-clays  and  pure  minerals  are  blended  in  the  manufacture  of 
wares.  The  compounding  of  the  white  ware  mixtures  and  the  processes 
for  their  manufacture  can  now  be  said  to  have  emerged  from  the  strictly 
empirical  stage  and  to*  have  reached  a  degree  of  perfection  that  cor- 
rectly merits  the  designation  of  "applied  science." 

In  the  brick,  tile  and  kindred  industries  which  use  more  complex 
clays — clays  that  naturally  contain  sufficient  fluxes  to  produce  the 
requisite  degree  of  hardness  in  the  burned  ware — ceramics  has  de- 
veloped principally  along  the  first  line,  the  application  of  mechanical 
principles  to  the  processes  of  manufacture.  In  this,  ceramics  has 
kept  abreast  of  the  demands.  Along  the  second  line,  the  application 
of  pure  science  to  the  determination  and  control  of  the  properties  of 
body  mixtures,  but  very  little  progress  has  been  made.  In  this,  science 
has  been  baffled  by  the  complexity  of  the  mineral  mixture  which  nature 
has  compounded  and  man  calls  clay. 

Complexity  of  properties  is  the  natural  result  of  complexity  of  min- 
eral composition.  If  this  complexity  of  mineral  composition  resulted 
simply  in  variation  of  chemical  constituent,  the  problem  would  be  com- 
paratively simple,  but  the  physical  properties  of  each  of  the  several 
minerals  are  nearly,  if  not  equally,  as  potent  factors  in  complicating 
the  problems,  as  the  chemical. 

133 


134  PAVING   BRICK   AND    PAVING    BRICK   CLAYS.  [bull.  no.  9 

The  science  of  ceramics  is  making  rapid  progress  in  the  solution  of 
these  problems;  but  today  the  question  of  what  physical  and  chemical 
properties  raw  clay  must  possess  that  it  might  be  suitable  for  use  in  the 
manufacture  of  paving  brick  is  still  unanswerable.  Chemical  analysis 
alone  is  not  a  safe  criterion  by  which  to  decide  this  and  similar  ques- 
tions, for,  as  can  be  shown  in  nearly,  if  not  all,  geological  survey  re- 
ports on  clays,  the  analyses„  of  clays  that  are  known' to  be  suitable  for 
paving  brick  have  their  counterparts  in  analyses  of  building  brick  clays. 
Indeed  in  range  of  variation  in  chemical  constituents,  these  two  types 
of  clays  overlap  one  another  to  a  very  large  extent.  There  are  possibly 
one  or  two  characteristics  in  the  chemical  composition  of  paving  brick 
clays  that  are  not  common  to  those  used  for  building  brick,  and  yet  no 
fixed  rule  has  been,  or  so  far  as  the  writer  can  perceive,  can  be,  laid 
down  at  present,  by  which  to  identify  paving  brick  clay  by  chemical 
analysis. 

Physical  tests  on  green  or  unburned  clay,  so  far  as  is  now  known, 
would  not  lead  one  any  nearer  the  possibility  of  fairly  judging  a  pav- 
ing brick  clay  than  would  chemical  analysis.  Possibly  an  exception 
should  be  made  of  determinations  of  fineness  of  grain.  Plasticity, 
tensile  strength,  bonding  power,  slaking  properties,  etc.,  are  found  to 
vary  widely  in  different  paving  brick  clays,  so  that  no  dependence  can 
be  placed  upon  any  of  them,  taken  alone.  The  determination  of  fine- 
ness of  grain,  however,  does  give  a  negative  test  that  seems  to  be  of 
some  value. 

Fine  grained  clays,  as  will  be  seen  later,  have  not  proved  to  be  good 
paving  brick  clays.  It  cannot  be  said,  however,  that  all  coarse  grained 
clays  are  good  paving  brick  clays.  Indeed,  although  evidence  is  lack- 
ing, there  is  no  obvious  reason  for  believing  that  any  hard  and  fast 
rule  can  at  present  be  laid  down  in  regard  to  either  fine  or  coarse 
grained  clays. 

When  the  history  of  a  few  paving  brick  plants  in  various  parts  of 
this  country  reveals  the  fact  that  experienced  paving  brick  manufactur- 
ers have  so  misjudged  a  deposit  of  clay  as  to  erect  an  extensive  plant 
upon  a  particular  site  and  soon  find  that  they  must  abandon  the  idea 
of  attempting  to  make  any  other  than  a  building  brick,  it  must  be  in- 
ferred that  even  a  burning  test  as  ordinarily  conducted  by  ceramic 
engineers,  surveys  and  brick  machine  manufacturers  -likewise  often 
gives  evidence  that  is  untrustworthy.  By  what  means  then  can  the 
suitability  of  a  clay  for  paving  brick  purposes  be  ascertained? 

It  was  with  hopes  of  obtaining  evidence  upon  this  problem  that  the 
Survey  undertook  a  study  of  the  properties  of  the  clays  and  burned 
bricks  of  several  of  the  leading  paving  brick  manufacturies  in  the 
middle  west,  together  with  several  samples  of  clays  from  various  parts 
of  this  state,  that  are  not  now  being  used  for  paving  brick  manufacture. 

For  many  years  scientists  have  been  devising  methods  with  which 
to  determine  the  cause  and  effect  of  the  various  properties  of  clay,  but 
they  have  not  made  much  progress.  For  instance,  the  reason  why  a 
kaolin  and  a  ball  clay,  having  similar  chemical  composition  and  size 
and  apparently  character  of  grain,  should  differ  so  widely  in  plasticity, 


purdy]  QUALITIES   OF   CLAYS   FOR   MAKING    PAVING   BRICK.  135 

is  still  an  open  question.  The  refractoriness  of  a  clay  is  still  incal- 
culable from  analytical  data,  although  exhaustive  researches  have  been 
made  to  determine  the  pyro-chemical  effect  of  inorganic  acids  and  bases, 
singly,  collectively,  and  in  mixtures,  with  standard  clays  and  com- 
pounds. "While  from  these  pyro-chemical  studies  it  has  been  shown 
that  the  fluxing  power  of  the  bases  is  roughly  proportional  to  their  mole- 
cular weight,  and  that  the  several  acids  operate  in  a  definite  manner,  so 
that  synthetical  mixtures  can  be  made  with  assurance  that  each  compon- 
ent will  operate  in  a  given  manner,  and  that  the  resultant  effect  of  the 
mixtures  will  in  general  be  as  presupposed,  similar  natural  mixtures, 
known  as  clays,  exhibit  properties  that  are  in  the  large  majority  of 
cases  entirely  contradictory  to  those  of  synthetical  mixtures,  due  no 
doubt  to  differences  in  the  physical  properties  of  the  minerals  as  well  as 
to  variation  in  mineral  content. 

Many  theories  have  been  advanced  concerning  the  geological  history  of 
clays,  and  general  statements  can  be  made  as  to  the  probable  conditions 
that  cause  the  breaking  down  of  the  parent  rock,  the  character  of  the  resi- 
dual debris,  the  agencies  sorting  and  transporting  this  debris,  and  the 
conditions  under  which  it  can  be  deposited  in  different  grades  of  fineness 
and  purity.  Geologists  can  state  with  considerable  accuracy,  the  effect  of 
vegetable  growth  and  of  ground  water,  the  cause  for  the  precipitation  of 
salts  from  solutions,  the  cementing  value  of  various  compounds  under 
different  conditions,  etc.  They  can  establish  the  fact  that  there  is  a  cycle 
of  rock  decomposition,  residual  deposition,  and  rock  formation  going  on 
constantly  en  masse,  as  well  as  in  the  small  grains  of  which  clay  and  soils 
are  composed.  Yet,  after  all,  neither  geologists  nor  chemists  are  able 
to  determine  the  exact  stage  of  breaking  down  or  building  up,  nor  the 
exact  combination  of  several  ingredients  existing  in  a  clay  at  the  time  of 
examination.  It  certainly  seems  patent  that  until  we  can  determine  the 
exact  mineralogical  condition  and  chemical  aggregation  of  a  given  clay 
it  will  be  impossible  to  use  the  analytical  data  obtained  by  ordinary  phy- 
sical and  chemical  tests  as  ground  for  predictions  concerning  its  probable 
pyro-chemical  behavior. 

In  the  process  of  any  chemical  analysis  known  to  the  writer,  the 
character  and  exact  identity  of  the  clay  as  a  whole,  as  well  as  its  con- 
stituent parts,  are  destroyed  by  the  disintegration  or  unlocking  of  the 
natural  combinations,  making  an  exact  .or  complete  determination  of  the 
chemical  conditions  originally  present,  a  mere  supposition.  In  fact 
all  we  know  or  can  learn  from  a  study  of  the  origin  and  mode  of  forma- 
tion of  clays,  and  of  the  alterations  in  their  composition  constantly  go- 
ing on  under  varying  conditions,  as  well  as  by  attempts  to  unlock  the 
combinations  or  separate  the  ingredients  by  chemical  methods  is,  that  we 
are  arresting  the  changes  of  transition  in  the  clay  from  one  state  to  an- 
other, but  are  not  able  to  ascertain  the  forms  or  conditions  existing  at 
that  time.  From  these  considerations  it  should  be  plain  that  two  samples 
of  clays  having  similar  origin  and  chemical  constitution,  may  differ  rad- 
ically in  their  mineralogical  make-up.  The  kind,  size  and  composition  of 
the  several  minerals  affect  so  materially  the  pyro-chemical  properties  of 
the  clay  as  a  whole,  that  until  mineralogists  can  find  means  of  determin- 


136  PAVING    BRICK   AND    PAVING   BRICK   CLAYS.  [bull.  no.  0 

ing  the  kind,  quantity  and  relative  size  of  the  several  mineral  ingredi- 
ents, ceramists  cannot  predict,  even  with  a  fair  degree  of  accuracy,  the 
behavior  of  a  clay  in  burning. 

Several  of  the  so  called  physical  properties  of  raw  clay  may,  however, 
be  measured  and  their  effect  on  the  behavior  of  the  clay  described.  In 
this,  physical  conditions  of  the  clay,  such  as  hardness,  fineness  of  grain, 
plasticity,  etc.,  are  by  custom  regarded  as  properties. 

The  properties  of  clays  may  be  classified  under  three  general  heads: 
Physical,  chemical,  and  pyro-chemical. 

PHYSICAL  PEOPEETIES. 
Introduction. 

Ceramists  have  tested  clays  by  all  the  means  that  have  been  suggested 
to  them.  Many  of  the  tests  have  proven  fruitless,  and  not  a  few  now  in 
use  are  of  doubtful  value. 

The  following  physical  tests  on  raw  clays  were  made  by  the  State 
Survey : 

1.  Specific  gravity  of  the  clay,  or  mineral  aggregate.  2.  Porosity  of  a 
dry,  unburned  brick  made  from  "stiff  mud."  3.  Drying  behavior.  4.  Shrink- 
age. 5.  Tensile  strength.  6  Fineness  of  grain.  7.  Water  of  plasticity. 
8.    Plasticity. 

Specific  Gravity, 
real  and  apparent  specific  gravity. 

The  determination  of  the  specific  gravity  of  a  clay,  if  made  at  all, 
should  be  so  conducted  that  the  result  would  be  a  composite  of  the  speci- 
fic gravities  of  the  several  minerals  that  make  up  the  clay  mass.  If  the 
specific  gravity  of  a  lump  be  taken  as  a  whole,  unless  the  mass  be  so 
thoroughly  saturated  that  each  grain  becomes  surrounded  by  the  saturat- 
ing medium,  it  would  vary  with  all  kinds  of  irregularities  incident  to  the 
processes  of  formation  or  manufacture.  The  first  method  would  give 
what  is  known  as  true  specific  gravity,  while  the  second  would  give  only 
an  apparent  value. 

The  writer  can  see  no  value  in  finding  the  apparent  specific  gravity, 
for,  as  a  means  of  detection  of  any  working  property,  it  is  absolutely 
valueless.  The  true  specific  gravity  may  have  direct  value  as  indicating 
some  working  property  of  the  clay,  but  if  it  has,  the  fact  has  not  been 
demonstrated.  The  data  for  the  true  specific  gravity  can,  however,  be 
used,  as  will  be  demonstrated  later,  in  the  analysis  of  some  of  the  changes 
that  take  place  in  drying  and  burning,  and  serves  as  a  check  on  the 
accuracy  of  some  of  the  other  data. 

METHODS   OF  DETERMINATION. 

The  true  specific  gravity  of  the  clays  included  in  this  report  was  ob- 
tained by  three  methods:  By  Seger  volumeter,  using  unburned  bricks; 
by  pycnometer;  by  chemical  balance,  using  unburned  bricks. 

Determination  by  Seger  s  Volumeter. — Seger's  volumeter  was  used  in 
the  determination  of  the  volume  shrinkage,  porosity  and  specific  gravity 
on  the  several  clays,  as  noted  in  Table  I  . 


PURDY] 


QUALITIES    OF    CLAYS    FOE    MAKING    PAVING   BRICK. 


137 


cu.t: 

O  on 

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Percent 
variation. 


Average  . . . 


Minimum 


Maximum. 


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variation. 


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^fCMOO      •CM0000©OSt-HOOSCOOS 


CMi-HCM      'OHrtHONHlONO      ••«# 


COCMlO00-»tl00CMt--^t~lO©lO-<#         CO  00  00  IO  00 

t-^os«5  0JNOcOiio»t-oi-i-'*iocnoto 

CMi-d-d-HCMCMi-li-ICOCMeMOOrHeCCMCMOOeMiH 


Minimum 


iHHN      'OHHrtONi 


■OOCOCMOxJHOOOOOCO©COO©CNII 
'  -"*  CM  i-l  r-C  i-H  CM  CM  fHi-HCMCMCMCMt-HOOCMCMOOi 


Maximum. 


ICM      'OrtMHONHmNO      •«*NNHNNC<IHHMC<INMi-lx)INNT|lWrH 


Per  cent 
variation 


©H01t">*10C 


)OCOt-©C~t-t~i-HCMt-O00eM0000CM^eM«©00©0000t-CMC<I 


Average. 


00  IO 
>  CM  CO  < 

^CO^CDOOt^C-xjIOOas'^OOCOOOCOC-COOOOOOOOO^Ir-^CO^COCOCOCOlOOOOO-HM 


Minimum.. 


COCMlOOOOOOO-^eMT-lt-OOOO^lO-^OOCMr-ICOi-iCMlO-^HrtCJlO-^^HOOOi-lOOOOTlO 


Maximum 


CO  o 

COCDOanO-*OSCD05'*^Ot-ONCDOSOCO-*Ot-050aOCO'HCOIOOCOCOCCOOC>5 
lOt-t-COOOt-t--^.00©ift-*<CO-*t-t-C--*OOOOlO-^t—  CMCO-*t-COCDC~COOOOO-HOO 


Sample  number. 


•     ••••••■      "OhNC^xJiiO       ......       ..     ,.     ..     ,  HH  jj  [J  CO  t-*  OO  O  **H  OO  X^H 

T-lWW*mOt-OOOSrtrHrHTH«i-l_|NrtCMM^rH     i       ,      I    I— I         "rHi-lrtCNJCMCMCM 


Kiln  Letter. 


iWa3QZo,J^OJta§^.u3JOwhP>Q  :  :  :  :  :  ^^>"^XN^ 


138  PAVING    BRICK   AND    PAVING    BRICK   CLAYS.  [bull.  no.  9 

The  accuracy  of  the  tests  in  the  volumeter  is  shown  in  Table  I  by  the 
percentage  of  variation  volume  shrinkage,  specific  gravity  and  porosity. 
These  variations  are  very  small  considering  the  conditions  under  which 
the  determinations  were  made. 

The  specific  gravity  of  any  substance  is  the  ratio  of  the  weight  of  that 
substance  to  the  weight  of  an  equal  volume  of  some  substance  taken  as  a 
standard.  In  the  metric  system  distilled  water  at  4°C.  is  taken  as  the 
standard.  At  this  temperature  a  cubic  centimeter  of  distilled  water 
weighs  one  gram.  Therefore,  when  rising  this  system,  volume  and 
weight  of  water  may  be  interchanged,  i.  e.,  1  c.c.=l  gram. 

With  this  understanding  the  formula  by  which  the  specific  gravity  of 
a  clay  can  be  obtained  could  be  expressed  as; 

-^    -    Sp.  gr. 

where  W— dry  weight  in  grams  and  V=volume  in  cubic  centimeters.  If 
the  porosity  of  the  brick  has  been  determined  the  formula  for  the  specific 
gravity  could  be  written : 

w 

=    bp.  gr. 

V   (100— P)  b    & 

Where  W=dry  weight  as  before,  V=volume  of  the  brick  in  cubic 
centimeters  and  P=pereentage  porosity. 

It  will  be  noted  by  comparing  the  specific  gravities  in  Tables  I  and 
II,  that  those  obtained  by  the  volumeter  are  lower  than  those  obtained  by 
the  pyenometer.  This  can  be  accounted  for  perhaps  by  the  operator's  in- 
ability completely  to  saturate  a  brick,  that  is,  to  fill  all  the  pore  spaces 
with  oil  without  resorting  to  the  use  of  a  suction  or  vacuum  pump  to  re- 
move all. the  air  from  the  pores  so  that  oil  could  enter.  If  the  air  is  not 
entirely  exhausted  it  will  pass  through  the  oil  very  slowl}T,  requiring  a 
period  extending  over  several  weeks  in  which  to  esape.  In  ordinary  labor- 
atory practice  sufficient  time  can  not  be  given  to  permit  the  complete  es- 
cape of  the  included  air.  In  the  porosity  and  specific  gravity  tests  here 
reported,  no  attempt  was  made  to  fill  the  pores  completely.  The  bricks 
were  simply  soaked  in  coal-oil  for  48  hours,  with  one  face  exposed  at  the 
level  of  the  surface  of  the  oil.  This  incompleteness  of  saturation  under 
these  conditions  is  shown  by  the  difference  in  the  specific  gravity  as  de- 
termined by  the  volumeter  and  pyenometer. 

Determination-  by  Pyenometer. — A  pyenometer,  or  specific  gravity 
bottle,  as  it  is  often  called,  is  a  small  flask  of  known  capacity,  usually 
25  to  100  c.c.  When  filled  up  to  a  given  mark  with  air-free  water  at 
normal  room  temperature,  its  weight  is  noted.  The  flask  is  then  partly 
emptied,  a  known  weight  of  clay  added,  and  the  whole  carefully  boiled  to 
exclude  all  the  entrapped  air,  then  cooled,  filled  up  to  the  mark  and 
weighed.  By  the  formula,  weight  of  dry  sample  (a)  plus  weight  of 
bottle  filled  with  cold  air-free  water  (b)  minus  weight  of  bottle  filled 
with  sample  and  water  (c),  or  a-}-b — c,  will  give  the  weight  of  water 
having  the  same  volume  as  the  sample  or  true  total  volume  of  the  clay 
particles.  Knowing  the  dry  weight  and  true  volume  of  the  grains,  their 
composite  specific  gravity  is  readily  calculated  by  the  formula  (dry 
weight  ~  volume). 


PURDY]  QUALITIES   OF   CLAYS    FOR    MAKING    PAVING   BRICK. 


139 


This  may  be  illustrated  by  the  following  calculation : 
Weight  of  bottle  filled  with  water  =  143.22. 
Dry  weight  of  sample  =  3.41. 

Weight  of  bottle  +  sample  +  water  required  to  fill  to  mark  =  145.35. 
143.22  +  3.41  —  145.35  ==  1.28    total  volume  of  the  particles. 
3.41  -J-  1.28  —  2.68    specific  gravity  of  the  sample. 

In  the  following  table  will  be  found  specific  gravity  of  the  clays  by  the 
pycnometer  method. 

TABLE  II. 


I 

II 

Average 

K    1  Alton,  111 

2.666 
2.602 
2.688 
2.667 
2.676 
2.661 
2.643 
2.693 
2.701 
2.683 

2.664 

2  527 

2.684 

2.668 

2.626 

2.664 

2.63 

2.685 

2.703 

2.689 

2.665 

K    2  St.  Louis,  Mo 

2.564 

K    3  Albion.  Ill 

2.686 

K    4  Springfield,   111 

2.667 

K    5  Edwardsville,  111 ... 

K    6Galesburg,  111 

2.651 
2.663 

K    7  Streator,  111 

2.636 

K    8  Veedersburg,  Ind 

2.683 

K    9  Crawfordsville,  Ind  

2.702 

K  lOTerre  Haute,  Ind 

2.686 

K  11  Brazil,  shale 

K  12  Brazil,  tire  clay 

2.667 
2.682 
2.633 
2.719 
2.633 
2.719 
2.655 
2.720 
2.643 
2.717 
2.708 
2.660 
2.608 
2.700 
2.653 
2.628 
2.718 
2.718 
2.683 
2.702 
2.668 
2.699 
2.666 
2.704 

2.671 
2.708 
2.646 
2.713 
2.632 
2.712 
2.656 
2.722 
2.646 
2.716 
2.710 
2.654 
2.591 
2.690 
2.690 
2.624 
2.715 
2.715 
2.685 
2.707 
2.676 
2.697 
2.668 
2.707 

2.669 

K  13  Clinton,  Ind 

2.695 

K  14  Western  Brick  Co 

2.639 

K  15  Barr  Clay  Co.,  Streator,  111 

2.716 

R    1  Nelsonville,  O 

2.633 

R    2  Portsmouth,  O 

2.715 

R    3  Canton  Imperial 

2.655 

R    4  Canton  Royal 

2.721 

S     1  Moberly,  Mo 

2.643 

S     2  Kansas  Citv,  Mo 

2.717 

F    1  Danville  Brick  Co 

2.709 

H  24  Carbon  Cliff,  fire  clay 

2.657 

H  17LaSalle,  111 

2.599 

H  16  Peoria,  111 

2.695 

H  18Sterling,  111 

2.671 

H  23  Carbon  Cliff ,  shale 

2.626 

H  21  Galena,  111 

2.717 

H  20  Savanna,   111 

2.717 

2.684 

L-II  Lawrence,  Kan 

2.705 

Ill  Casey,  Kan 

2.672 

J-II  Pittsburg,  Kan 

2.698 

2.667 

G-II  Coffeyville,  Kan.     . 

2.706 

Determination  with  Chemical  Balance. — The  dry,  saturated  and  im- 
mersed weights  of  briquettes  were  determined  by  using  a  chemical  bal- 
ance. For  this  it  was  found  that  briquettes  of  the  *size  %' 7x%' '^V'2 
could  be  used.  Obviously  the  larger  the  briquette  the  more  nearly  true 
will  be  the  determined  specific  gravity.  Sizes  larger  than  that  given, 
however,  cannot  be  used  to  advantage  on  the  ordinary  chemical  balance. 
This  method  was  used  for  but  a  small  number  of  samples. 

The  briquettes  were  dried  to  constant  weight  in  an  air  bath  at  120 °C. 
cooled  in  a  dessicator  and  their  dry  weight  obtained  as  rapidly  as  possible. 
After  weighing,  the  briquettes  were  immersed  in  clarified  coal-oil  with 
one  face  above  the  level  of  the  oil.  After  standing  thus  for  20  to  24 
hours,  they  were  placed  under  a  bell  jar  and  the  air  kept  exhausted  for 
fifteen  minutes,  it  having  been  found  in  previous  work  that  this  treat- 
ment was  sufficient  to  attain  nearly  complete  saturation.  The  briquette 
was  then  suspended  by  a  silk  thread  from  the  beam  of  a  chemical  bal- 


140 


PAVING    BRICK   AND    PAVING    BRICK   CLAYS. 


[BULL.    NO.    9 


ance  and  its  saturated  weight  noted.  A  breaker  partially  filled  with  oil 
was  then  so  placed  that  the  briquette  could  swing  clear  and  be  com- 
pletely immersed.  In  this  manner  the  immersed  weight  of  the  briquette 
was  obtained. 

By  the  formula  then  of  dry  weight  (D)  divided  by  (dry  weight  (D) 
minus  suspended  weight  (S)  )  orD-f  (D— S),  the  specific  gravity  of 
the  material  in  the  briquette  was  readily  obtained. 

The  comparative  accuracy  attained  in  the  determination  of  the  speci- 
fic gravity  of  clay  by  these  three  methods  may  be  seen  in  the  table  fol- 
lowing. 

Table  III. 


Volumeter- 
Average. 

Pycnometer— 
Average. 

Chemical 
Balance. 

Average  of 
three 

Max. 

Min. 

determina- 
tions. 

K    1 

2.54 
2.60 
2.58 

2.66 
2.64 
2.67 

2.614 

2.69 

2.63 

2.616 

2.57 
2.58 

2  615 

K  14 

2  65 

K    4 

2  61 

It  is  evident  from  this  table  that  the  essential  fault  in  the  first  and 
third  method  of  determining  specific  gravities  lies  in  the  fact  that  the 
brick  was  not  completely  saturated,  and  therefore,  gave  low  specific 
gravities.  The  closeness  in  agreement,  however,  suggests  that  by  the  use 
of  extra  precaution  in  the  saturation  of  the  bricks  the  specific  gravities 
of  the  clays  could  be  made  quite  accurately  by  either  of  these  two 
methods. 

Porosity. 


DEFINITION". 

The  percentage  of  porosity  expresses  the  relation  between  the  volume 
of  pore  space  and  the  combined  volume  of  the  particles  of  which  the 
clay  is  composed.  It  is  the  ratio,  in  terms  of  volumes,  of  void  spaces  to 
solid  particles.  If  determined  on  an  unburned  brick  it  would  measure 
the  degree  of  consolidation  of  the  mass. 

METHOD  OF  DETERMINATION. 

The  porosity  of  an  unburned  clay  mass  may  be  determined  directly  by 
two  methods :  first,  by  use  of  the  Seger  volumeter ;  second,  by  the  use  of 
a  chemical  balance,  and  indirectly,  or  by  calculation  on  basis  of  the 
pycnometer  specific  gravity  determination. 

To  obtain  percentage  of  porosity  by  either  of  the  direct  methods,  the 
briquette  or  lump  must  be  dried  to  constant  weight,  and  the  dry  weight 
obtained,  then  saturated  in  kerosene  and  the  saturated  weight  obtained. 
The  difference  between  the  saturated  and  dry  weights  is  obviously  the 
weight  of  petroleum  that  is  required  to  fill  the  pores.  This  weight 
divided  by  0.8,  the  density  of  the  oil,  gives  the  equivalence  of  oil  in 


PURDY]  QUALITIES   OF   CLAYS    FOR    MAKING    PAVING   BRICK.  141 

terms  of  water.  Thus  far,  therefore,  the  actual  amount  of  pore  space  in 
the  brick  in  terms  of  water  by  weight  is  known.  If  the  metric  system 
has  been  used  throughout,  this  amount  of  water  by  weight  is  equivalent 
to  its  amount  by  volume,  since  one  cubic  centimeter  of  water  at  room 
temperature  weighs  practically  one  gram. 

Complete  saturation  of  a  lump  of  unburned  clay  even  with  kerosene, 
for  which  clay  seems  to  have  a  peculiar  physical  attraction,  cannot  be 
obtained  without  resorting  to  the  use  of  a  vacuum  pump.  Standing  in 
oil  for  48  hours  is  not  sufficient  to  cause  complete  saturation,  as  has  been 
shown  on  preceeding  pages  by  the  specific  gravity  so  obtained,  as  well 
as  by  the  discrepancy  between  the  directly  measured  and  the  calculated 
porosity  as  given  in  table  IV,  page  144. 

In  obtaining  the  dry  and  saturated  weights,  the  two  direct  methods 
are  alike.  The  data  for  actual  volume  of  the  pores  thus  obtained  are, 
however,  of  no  value  in  themselves,  and  cannot  become  of  value  until 
calculated  to  parts  of  100  unit  volumes  of  the  whole  brick.  For  this, 
it  is  more  practical  to  determine  the  volume  of  the  whole  mass,  i.  e., 
pores  plus  solid  particles.  It  is  in  the  determination  of  the  volume  of 
the  mass  that  the  two  direct  methods  above  mentioned  are  differen- 
tiated. 

First  method,   Volumeter. — After  complete   saturation,   the  brick   is 
placed  in  the  volumeter  and  its  volume  determined  in  cubic  centimeters. 
W— S 

Bv  the  formula  100  ( )  where  W=weight  of  oil  taken  up  by  the 

V 
brick,  S=the  specific  gravity  of  the  oil,  and  V=the  volume  of  the  brick, 
there  is  expressed  the  part  of  100  unit  volumes  of  the  brick  as  a  whole 
which  consists  of  open  pore.     In  other  words,  it  is  the  percentage  por- 
osity. 

By  referring  to  Table  I  it  will  be  noted  that  the  percentage  of  varia- 
tion in  the  porosity  determination  was  relatively  small.  Since  the  data 
given  in  Table  I  represents  determinations  made  on  60  bricks  of  each 
clay  47.5  as  the  maximum,  0.6  per  cent  as  the  minimum,  and  11.5 -as 
the  average  percentage  variation,  is  considered  as  being  excellent. 

These  percentages  of  variation  in  results  are  not  surprising  in  view  of 
the  fact  that  an  error  of  lcc.  in  determination  of  volume,  or  an  error 
of  1  gram  in  obtaining  either  the  dry  or  saturated  weight,  makes  a  dif- 
ference of  0.3  in  the  porosity. 

It  is  obvious,  therefore,  that  when  the  dry  weight  of  the  bricks  are 
obtained  they  must  be  absolutely  dry,  i.  e.,  oven  dried  at  120° C.  so  as 
to  expel  all  of  the  hygroscopic  water.  This  was  not  done  in  obtaining 
the  data  given  in  Table  I. 

Second  method,  Chemical  Balance. — When  the  porosity  of  the  brick 
is  determined  on  a  chemical  balance  the  volume  of  the  briquette  is 
found  by  the  apparent  loss  of  weight  of  the  briquette  when  suspended 
in  the  oil.  The  briquette  appears  to  lose  weight  when  thus  suspended, 
and  this  loss  of  weight  is  equivalent  to  the  weight  of  a  quantity  of  oil 


142  PAVING   BRICK   AND    PAVING   BRICK   CLAYS.  [bull.  no.  9 

equal  to  that  of  the  briquette.  This  method  was  used  by  Dr.  E.  E. 
Buckley  in  the  test  on  the  Wisconsin  clays,  and  the  porosity  calculated 
by  him  using  the  formula: 

100  J  ^ - — P'  *    — .  =  per  cent  of  porosity. 

|(W— D)  Sp.gr. +  D        P  l  y 

In  this  formula  W=saturated  weight;  D=dry  weight;  and  Sp.  gr.  the 

composite  specific  gravity  of  the  clay  particles,  as  calculated  from  dry, 

saturated,  and  suspended  weights  of  the  briquette. 

This  formula,  however,  can  be  simplified  by  substituting  for  the  value 

'of  D  in  the  denominator  its  value  in  terms  of  the  Sp.  gr.  and  suspended 

weight   (S)   as  given  in  the  formula  for  specific  gravity  where  D=D 

(Sp.  gr.)-S   (Sp.  gr.). 

rw— d] 

The  Buckley  formula  then  simplifies  to  the  expression  100  < >= 

lw-sj 

porosity.  This  formula  holds  true  no  matter  what  liquid  is  used  in  the 
saturation  of  the  brick,  so  long  as  the  same  liquid  is  employed  in  ob- 
taining the  suspended  weight. 

The  method  is  accurate  but  very  slow  and  tedious,  unless  it  is  carried 
out  with  small  pieces  on  the  jolly  balance. 

If  a  jolly  balance  is  used  in  this  determination,  the  weight  of  the  bri- 
quette or  piece  must  not  exceed  that  which  would  stretch  the  spring  be- 
yond its  elastic  limit.  If  any  other  than  a  light  weight  spring  is  used  the 
difference  between  the  several  readings  will  not  be  sufficient  to  permit  of 
very  accurate  determination.  This  method  was  used  in  the  determina- 
tion of  the  rate  of  vitrification,  which  will  be  described  under  the  gen- 
eral heading  of  "Pyro-Chemical  Tests/'  so  will  not  be  discussed  in  de- 
tail at  this  time. 

Third  Method,  Calculation. — It  has  been  noted  that  the  specific  grav- 
ity of  the  powdered  clay  by  the  pyenometer  method  is  uniformly  higher 
than  that  calculated  from  data  obtained  on  the  green  bricks.  It  has 
also  been  noted  that  this  difference  between  the  specific  gravities  is  due 
to- the  incomplete  saturation  of  the  brick.  Since  the  formula  for  speci- 
fic gravity  is:  Dry  weight  (W)   divided  by  the  combined  volume  of  the 

W 
particles   (V)   or  — =Sp.  Gr.,  the  true  volume  of  the  particles  in  the 

V 
brick  can  be  obtained  bv  the  formula :   Dry  weight  divided  bv  the  pveno- 

D 

meter  specific  gravity,  or =Vol.     Then  the  volume  of  the  whole 

Sp.  Gr. 
brick  (Vb)  minus  the  volume  of  the  clay  particles  (Yc)  would  give  the 
volume  of  the  pore  spaces   (Vp),  or  Vb — yc=VPt.     To  obtain  the  frac- 
tional amount  of  pore  space  in  a  brick,  the  volume  of  the  pores   (Vp) 


purdy]  QUALITIES   OF   CLAYS   FOR    MAKING    PAVING   BRICK.  143 

Vp  Yb — Yc 

must  be  divided  by  the  volume  of  the  brick,  or  — .     But  since = - 

yb  yb 

yp  f       yc]  W 

—  we  have  100  ]1 !-=per  cent  pore  space  where  Vc= 

Yb  [       VbJ  Sp.  Gr. 

The  economy  and  accuracy  in  determining  porosity  by  this  method 
lies  in  the  fact  that  it  is  not  necessary  to  saturate  the  brick  and  obtain 
the  saturated  weight.  It  is  obvious,  therefore,  that  the  bricks  would 
either  have  to  be  partially  saturated  or  covered  with  a  thin  coating  of 
paraffin  and  their  volume  determined  in  a  volumeter.  Without  a  volu- 
meter this  method  cannot  be  used. 

If  the  specific  gravity  has  been  determined  by  the  pycnometer  method 
and  a  volumeter  is  not  accessible,  the  porosity  is  best  calculated  by  the 
Buckley  formula.  In  this,  however,  complete  saturation  of  the  brick 
must  be  assured,  and  the  true  specific  gravity  of  the  clay  particles  used. 

Neither  the  Buckley  method  nor  the  indirect  method  here  proposed 
is  usable  on  any  other  than  a  green  or  unburned  lump  of  clay.     For  the 

fW-Dl 

porosity  of  a  burned  lump  or  briquette,   the   formula    100   \ }■    is 

[  W— S  J 
the  only  one  that  will  give  accurate  results,  as  will  be  shown  under  the 
discussion  of  Pyro-Chemical  and  Physical  Properties  of  Clays. 

In  the  following  table  are  given  porosity  data  obtained,  first,  by  the 
usual  volumeter  method  without  taking  into  account  the  hygroscopic 
water;  second,  by  the  indirect  method  described  above,  without  taking 
into  account  the  Irygroscopic  water,  and  third,  by  the  indirect  method  on 
a  basis  of  absolute  dryness  of  the  bricks.  The  percentage  of  increase  of 
porosity  obtained  in  the  second  and  third  instance,  over  that  obtained 
in  the  first  is  also  shown. 


144 


PAVING    BKICK    AND    PAVING    BRICK   CLAYS. 


[BULL.    NO.    9 


Table  IV — Showing  the  percentage  of  errors  in  the  Seger  Volumeter 
method  of  determining  porosity  as  customarily  executed. 

Calculated  results  are  by  the  indirect  method. 


Sample 

Dry  weight 

in 

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C 

CD 

1 

p 

V 

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o 

o 

a 

<D 

£ 

3 

O 
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a 

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In 

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c  w 
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.-,  a, 
9  3 

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0* 

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Ph 

a 
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a 
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3  $5 

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"3S. 
%& 

"S'Q 

Oh 

o"3 

Ph 

0  <v 

IS 

a  a 

be.  > 
Ph 

a 
0 

|| 

3  3 

*| 

?s 

00 

Ph 

Percentage  increase  by  cal- 
culation on    overdried 
briquettes    over    that    by 
volumeter    on    air    dried 
briquettes. 

and 
Brick  Number. 

O) 

-S 

M 

< 

.a 

a 
> 
0 

K  3—34 

571.5 
572.5 
601.3 
644.9 
647.1 
658.4 
607.4 
586.5 
600.4 
663.7 
631.2 
621.5 
545.5 
539.9 
532.2 
622.4 
600.7 
619.5 
639.2 
637.0 
642.9 
583.0 
588.2 
579.4 
601.0 
650.5 
600.5 
687.1 
667.0 
690.9 
705.6 
678.1 
716.1 
575.5 
573.0 
565.5 
599.0 
612.2 
602.3 
708.7 
705.3 
712.3 

556.4 
558.0 
587.7 
639.3 
640.7 
652.7 
596.6 
574.0 
587.5 
652.4 
620.7 
611.7 
533.2 
523.5 
520.0 
607  9 
587.8 
605.9 
625.3 
624.0 
629.6 
567.4 
576.3 
563.5 
591.4 
640.0 
591.5 
672.9 
653.9 
678.7 
689.2 
663.0 
697.8 
545.7 
541.5 
540.0 
584.2 
591.4 
584.4 
702.6 
696.8 
704.0 

300.2 
297.8 
311.5 
329.5 
330.6 
337.4 
327.7 
312.1 
323.4 
336.6 
320.7 
316.3 
284.6 
281.6 
278.8 
323.6 
310.3 
322.0 
315.6 
314.3 
317.1 
300.1 
303.2 
296.6 
291.4 
314.4 
292.9 
344.3 
336.3 
348.5 
348.7 
337.0 
352.0 
309.5 
307.2 
303.8 
322.6 
326.7 
324.8 
349.7 
347.8 
349.6 

23.0 
24.0 
23.8 
25.6 
25.4 
25.5 
27.3 
26.3 
26.9 
24.3 
24.1 
24.1 
25.0 
24.7 
25.7 
26.6 
26.6 
28.4 
21.8 
22.1 
21.7 
23.0 
23.0 
23.0 
17.5 
17.6 
18.3 
23.2 
23.0 
23.1 
20  3 
21.2 
20.3 
21.2 
20.0 
21.5 
26.0 
23.9 
25.6 
22.5 
22.7 
22.7 

29.12 
28.43 
28.13 
26.17 
26.17 
26.39 
29.69 
28.71 
29.57 
26.67 
26.81 
26.93 
28.64 
28.62 
28.94 
28.63 
28.17 
28.61 
24.17 
24.12 
24.09 
28.49 
28.59 
28.09 
22.38 
22.13 
22.84 
24.83 
25.30 
25.33 
25.64 
26.05 
25.24 
29.70 
29  48 
29.62 
31.35 
30.72 
31.44 
24.67 
25.03 
24.68 

26.61 

18.45 

18.19 

2.22 

3.03 

3.49 

8.76 

9.16 

9.93 

9.75 

11.24 

11.75 

14.56 

15.87 

12.60 

7.63 

5.90 

6.27 

10.87 

9.14 

11.01 

23.87 

24.30 

22.13 

27.88 

25.74 

24.81 

7.03 

10.00 

9.65 

26.31 

22  88 

24.34 

40.09 

47.40 

37.77 

20.57 

28.53 

22.81 

9.64 

10.26 

8.27 

31.0 

30.24 

29.76 

26.81 

26.89 

27.03 

30.94 

30.23 

30.08 

27.92 

28.03 

28.08 

30.25 

30.79 

30.56 

32.10 

29.71 

30.18 

25.82 

25.67 

25.67 

30.40 

30.03 

30.06 

23.62 

23.38 

23.99 

26.39 

26.76 

26.65 

27.36 

27.70 

27.15 

33.34 

33.36 

33.80 

33.03 

33.10 

33.47 

25.32 

25.93 

25.55 

34  78 

K  3—37 

26  00 

K  3—39 

25  04 

K  5—13 

4  73 

K  5—15 

5  87 

K  5-17  .. 

6  00 

K  7-  1 

K  7—  3 

13.34 
14  94 

K  7—  5 

11  82 

K  8—19 

14  89 

K  8—24 

16  31 

K  8—31 

16  51 

K10—  1 

21  49 

K10-  2 

24.66 

KIO—  4 

18.91 

K13— 44 

20.67 

K13— 46 

11.69 

K13— 53...' 

7.40 

H18-  1 

H18—  3 

18.44 
16.16 

H18—  5 

18.30 

H20—  1 

32.18 

H20—  3 

30.56 

H20—  4 

30.70 

H24—  1 

34.97 

H24—  3 

32.84 

H24—  5 

31.09 

R  3—  1 

13.75 

R  3—  3 

16.35 

R  3—  5 

15.37 

R  4—26 

34.78 

R  4—29 

30.66 

R  4—36  . . . 

33.74 

S    1—  1 

52.55 

S    1—  3 

66.80 

S    1—5 

57.20 

L-II-11 

L-II-13, 

27.04 
38.40 

L-II— 15 

30.74 

G-II— 55  .... 

12.53 

G-II— 57  .     . 

14.23 

G-IT— 58 

12.56 

The  data  in  table  IV  shows  the  inaccuracy  of  the  usual  method  of  de- 
termining the  porosity  in  dried  clay  wares.  It  has  been  stated1  that  three 
to  six  hours  is  sufficient  to  saturate  with  oil  unburned  briquettes  that 
measure  dxiy^x1^  inches.  Forty-eight  hours  was  therefore  considered 
ample  time  in  which  to  saturate  a  brick  that  cubically  was  about  eight 
times  as  large.  From  the  fairly  close  agreement  in  the  specific  gravities 
as  determined  by  the  pyenometer  and  the  volumeter,  it  was  thought  that 
the  briquettes  had  been  fairly  well  saturated.  Such,  however,  was  evi- 
dently not  the  case. 

1  Iowa  Geological  Survey,  Vol.  14, p.  18. 


PURDY] 


QUALITIES   OF   CLAYS    FOR    MAKING    PAVING    BRICK. 


145 


RELATION  OF  RATE  OF  ABSORPTION  TO  POROSITY. 

Aside  from  exposing  the  irregularities  in  our  method  of  analysis,  this 
data  gives  evidence  of  the  lack  of  relation  of  total  porosity  and  rate  of 
absorption  in  the  green  or  unburned  bricks.  Since  all  the  bricks  were 
subjected  to  the  same  oil  immersion  treatment,  it  must  follow  that  clays 
differ  in  the  rate  at  which  they  can  be  saturated,  and  that  this  rate  is 
not  wholly  a  function  of  porosity. 

The  writer  is  not  aware  of  tests  ever  having  been  made  to  investigate 
this  property,  which  we  may  call  "absorption  ratio,"  but  its  significance 
in  connection  with  the  drying  behavior  of  clays  is  obvious. 

Johnson1  has  said,  "Obviously,  too,  the  quantity  of  liquid  in  a  given 
volume  of  soil  affects  not  only  the  rapidity,  but  also  the  duration  of 
evaporation.  The  following  table,  by  Schubler,  illustrates  the  peculiar- 
ities of  different  soils  in  these  respects.  The  first  column  gives  the  per- 
centages of  water  absorbed  by  the  completely  dry  soil.  In  these  experi- 
ments the  soils  were  thoroughly  wet  with  water,  the  excess  allowed  to 
drip  off,  and  the  increase  of  weight  determined.  In  the  second  column 
are  given  the  percentages  of  water  that  evaporated  during  the  space  of 
four  hours  from  the  saturated  soil  spread  over  a  given  surface." 

TABLE  V. 


Per  cent. 

Percent. 

Quartz  sand 

25 
27 
29 
34 
40 
51 
52 
61 
70 
85 
89 
181 
256 

88.4 

Gypsum 

71.7 

Fine  sand 

75.9 

Slaty  marl 

68.0 

Clay  soil  (60  r:  clay) 

52.0 

Loam 

45.7 

Plough  land 

32.0 

Heavy  clay  (80  r'c  clay) 

34.9 

Pure  gray  clay 

31.9 

Fine  carbonate  of  lime 

28.0 

Garden  mould 

24.3 

Humus 

25.5 

Fine  carbonate  of  magnesia 

10.8 

"It  is  obvious  that  these  two  columns  express  nearly  the  same  thing 
in  different  ways.  The  amount  of  water  retained  increases  from  quartz 
sand  to  magnesia.  The  rapidity  of  drying  in  the  air  diminishes  in  the 
same  direction." 

Johnson  affirms2  that  "these  differences — (in  the  imbibing  power  of 
clays) — are  dependent  mainly  on  the  mechanical  texture  or  porosity  of 
the  material."  That  Johnson's  statement,  when  applied  to  unburned 
bricks,  is  incorrect,  is  shown  by  the  data  in  table  IV.  That  there  are 
other  factors  affecting  the  difference  in  rate  of  absorption  and  evapora- 
tion in  different  clays  is  quite  evident. 

Value  of  the  Porosity  Determination  on  Raiv  Clay  Lump. — It  has 
been  contended  at  various  times  in  ceramic  literature  that  a  porosity  de- 
termination on  a  raw  lump  of  clay  would  give  evidence,  concerning  such 
properties,   as   slaking,   weathering,   amount   of   water   required   to   de- 

1  Loc.  Cit.,  p.  18. 

2  How  Crops  Feed,  p.  175. 

—10  G 


146 


PAVING    BRICK   AND    PAVING   BRICK   CLAYS. 


[BULL.    NO.    9 


velop  plasticity,  etc.,  and  thus  indirectly  the  shrinkage.  Such  claims 
have  never  been  based  on  data,  nor  are  they  substantiated  by  the  data 
secured  by  this  Survey.  As  will  be  shown  in  later  paragraphs,  neither 
data  nor  sound  reason  would  warrant  such  statements. 

Value  of  the  Porosity  Determination  on  Green  Brick. — Before  the 
value  of  knowing  the  porosity  of  a  green  brick  can  be  discussed  it  is  neces- 
sary to  show  the  correlation  of  that  property  with  those  which  it  affects. 
If  porosity,  fineness  of  grain,  and  drying  behavior  are  in  any  degree  re- 
lated functions,  curves  plotted  from  data  should  show  such  relations. 
Such  a  relation  is  shown  in  Fig.  4  where  there  seems  to  be  an  inverse 
ratio  between  fineness  of  grain  in  surface  or  loose  grained  clays,  and  the 
porosity  of  the  green  or  unburned  brick.       The  data  from  which  this 


nn 

110 
100 

80 

70 

N, 

1 

8         1 

9         & 

i       2 

1         2 

2         2 

3         2 

4         2 

5          2 

S         2 

T          2 

3         2 

9         30 

FERVENT  POROSITY 

Fig.  4.  Curve  showing  relation  between  porosity  and  fineness  of  grain.   (From  data  of  Beyer 
and  Williams,  Iowa  Geol.  Surv.,  Vol.  14,  p.  123.) 

curve  was  plotted  was  obtained  from  the  work  of  Beyer  and  Williams1. 
The  surface  factor  was  calculated  from  their  data  by  the  method  given 
on  page  113.  The  porosity  data  and  calculated  surface  factor  are  as 
follows : 

TABLE  IV. 


Porosity. 


Surface  factor. 


Dale  Brick  Co 

Gethmann  Bros 

L.  C.  Besley  (bottom) 
L.  C.  Besley  (middle) 
L.  C.  Besley  (top)  .... 


18.14 
22.43 
24.03 
25.30 
29.77 


136.40 
114.38 
119.98 
100.48 

74.77 


This  reciprocal  relation  between  fineness  of  grain  and  porosity  could 
be  taken  as  evidence  in  proof  of  the  close  relation  of  fineness  of  grain 
and  porosity  of  the  green  brick  to  drying,  shrinkage  and  other  properties 
that  are  peculiar  to  wares  manufactured  from  fine  but  loose-grained 
clays  or  mixtures.     The  writer  hesitates,  however,  to  affirm  the  truth  of 


1  Iowa  Geol.  Surv.,  Vol.  XIV,  p.  123. 


PURDY] 


QUALITIES   OF   CLAYS   FOR    MAKING    PAVING    BRICK. 


147 


such  a  relation  from  evidence  obtained  on  a  few  samples  of  a  single  type 
of  clay.  Observation  of  the  working  behavior  of  boulder  clays  in  build- 
ing brick  manufacture  does  not  lead  one  to  believe  in  such  an  exact  rela- 
tion. 

In  the  manufacture  of  bricks  by  the  ordinary  dry  process — where  there 
is  present  only  from  6  to  12  per  cent  of  mechanical  water,  and  the  grains 
of  the  clay  are  not  surrounded  by  slippery  media  that  permit  the  particles 
to  slide  easily  and  freely  upon  one  another — the  clay  cannot  be  formed 
into  as  compact  a  mass  as  when  there  is  sufficient  water  present  to  permit 
of  manufacture  by  the  stiff  mud  process.  If  dry  pressed  bricks  be  formed 
in  a  hammer  machine,  or  press,  where  the  brick  is  subjected  to  repeated 
blows  by  a  heavy  hammer,  the  clay  particles,  even  though  nearly  dry, 
would  be  forced  over  one  another  until  the  mass  assumes  a  much  closer  or 
denser  structure  than  is  possible  by  the  ordinary  dry  press  process.  The 
difference  in  structure,  and  its  consequent  effect  on  the  burning  properties 
of  dry  press  bricks  manufactured  by  these  two  methods  in  the  St.  Louis 
district  is  more  evident  than  the  difference  between  the  structure  of  the 
dry  and  stiff  mud  or  stiff  mud  and  soft  mud  bricks. 

When  the  grains  are  made  to  lie  closer  together,  either  by  strong 
force,  or  by  a  lighter  force  supplemented  by  a  floating  medium,  better 
opportunity  is  offered  for  the  grains  to  fuse  with  one  another.  This  is 
shown  nicely  by  the  fact  that  hammered  brick  can  be  burned  in  the 
colder  parts  of  a  kiln  to  a  degree  of  hardness  that  is  equal  to  and  often 
exceeds  the  hardness  of  a  brick  made  from  the  same  clay  by  the  dry 
press  method  and  burned  in  the  hotter  portions  of  the  kiln. 

In  the  illustrations  just  cited,  the  difference  in  the  burning  properties 
of  bricks  made  from  the  same  clay  by  different  processes,  has  been  used 
as  a  means  of  noting  that  porosity  of  green  brick  is  not  wholly  a  func- 
tion of  size  of  grain.  It  is  clear  that  it  is  also  very  largely  a  function 
of  process  of  manufacture. 

While  there  may  be  some  relation  between  the  size  of  grain  of  loose 
or  soft  clays  and  the  porosity  of  the  brick  manufactured  from  them,  it 


OH  21 


H23 
6K 10 


OH20 


sK4. 


OH  I 


OKlJi 
ORl 


otfw 


o 

OK  11 


■jut, 


b A'  3 

$K2 


OR4. 


o    J 
Kl4 


m 


OKlL 


OKI 
OK9 


OK  6 


21  2J  25~ 

PERCENTA  CF.  POROSITY 


27 


Fig.  5.  Diagram  showing  the  relation  between  porosity  of  green  shale  brick  and  the  absolute 
fineness  of  grain.    (From  data  given  in  Table  I.) 


148  PAVING   BRICK   AND    PAVING   BRICK   CLAYS.  [bull.  no.  9 

is  still  doubtful  if  a  similar  relation  can  be  observed  in  the  hard  rock- 
like fossil  clays,  such  as  shales,  where  the  mineral  particles  are  so  cement- 
ed as  to  very  stubbornly  resist  separation  by  the  crushing  force  of  dry 
pan  mullers  as  well  as  the  disintegrating  influence  of  the  water  used  in 
pugging. 

In  Fig.  5  are  shown  curves  plotted  from  data  obtained  with  shales  in 
the  same  manner  as  the  data  for  surface  clays  in  Fig.  4.  The  porosity 
is  taken  from  Table  I,  and  the  surface  factor  from  Table  VIII. 

The  clay  from  which  these  shale  brick  were  made  had  been  crushed  to 
pass  through  a  dry  pan  and  then  screened.  In  the  laboratory  they  were 
known  as  dry  pan  samples.  These  "dry  pan  samples"  were  then  in  the 
same  state  of  mechanical  subdivision  as  the  clay  used  by  the  manu- 
facturer. 

In  making  the  bricks  from  which  the  data  in  Table  I  were  obtained, 
considerable  time  was  expended  in  pugging  or  wedging  the  clays  by 
hand,  first  in  a  large  bulk,  and  later  in  quantities  just  sufficient  for  one 
brick.  The  operator  batted  a  quantity  of  clay  that  would  make  approxi- 
mately 60  bricks  4%"x2:1/2/'x^%,/  on  a  plaster  top  table  until  it  was  as 
compact  as  he  could  make  it.  Then  by  use  of  a  trowel  in  some  instances 
and  a  wire  in  others,  he  cut  off  from  the  large  mass  a  quantity  sufficient 
to  fill  the  die  of  the  press.  This  smaller  piece  was  again  thoroughly 
wedged  by  hand  until  all  air  blebs  had  been  worked  out  and  the  whole 
took  on  the  shape  of  a  compact  loaf.  This  loaf  was  then  placed  in  the 
die,  using  care  to  see  that  it  cleared  the  sides  so  as  to  prevent  a  shearing 
off  of  any  portion  of  the  loaf  on  the  edge  of  the  die  when  the  plunger 
descended.  The  loaves  were  pressed  into  bricks  on  a  slow  screw  tile  press, 
so  that  the  clay  did  not  receive  much  compression,  but  yet  sufficient  to 
cause  it  to  flow  in  shreds  up  around  one  side  or  another  of  the  plunger. 
From  this  flowage  of  the  clay  past  the  plunger,  together  with  the  unusual 
amount  of  wedging  by  hand,  it  was  considered  that  the  clay  had  been  sub- 
jected to  a  treatment  that  was  approximately  comparable  to  the  pugging 
it  would  have  received  in  the  factory,  so  that  the  data  as  given  in  Table 
I  show  approximately  the  physical  structure  except  for  lamination  that 
would  be  developed  on  a  regular  manufacturing  basis. 

It  is  commonly  known  by  paving  brick  manufacturers  that  some  shales 
require  inordinate  pugging  before  they  develop  sufficient  plasticity  to 
permit  the  production  of  a  perfect  bar  in  the  die  of  the  brick  machine. 
In  fact  it  is  not  uncommon. to  see  a  battery  of  two  pug-mills  through 
which  the  clay  must  pass  before  it  enters  the  brick  machine  proper.  In 
the  brick  machine  the  clay  receives  further  pugging  before  it  issues  as  a 
bar  from  the  die.  It  is  also  not  uncommon  to  hear  the  manufacturers 
claim  that  they  cannot  pug  clay  sufficiently  unless  they  use  hot  water. 
Not  all  manufacturers  have  to  resort  to  this  extra  care  in  the  pugging 
process,  for  some  shales  develop  plasticity  with  sufficient  readiness  to 
allow  them  to  emerge  from  the  first  pug-mill  in  a  workable  condition. 
This  same  difference  in  the  working  property  of  the  various  shales  was 
perhaps  more  noticeable  in  the  laboratory  than  in  the  factories. 

This  difference  in  the  working  properties  of  shales  is  considered  to  be 
due  to  the  fact  that  the  grains  of  clay  are  cemented  by  substances  that 
differ  in  their  solubility  in  water.     It  is  now  well  known  that  soils  and 


purdyJ  QUALITIES   OF   CLAYS   FOR    MAKING   PAVING   BRICKS.  149 

clays  contain  soluble  salts  that  are  adsorbed  by,  or,  to  nse  a  more  homely 
expression,  smeared  over  the  particles,  and  are  not  easily  extracted  by 
water.  It  has  been  learned  by  experiment  that  clays  can  take  on  or 
adsorb  soluble  salts  from  solutions  and  so  retain  these  salts  in  their  sub- 
microscopic  pores  that  they  cannot  again  under  ordinary  conditions  be 
dissolved  from  the  clay. 

The  amount  of  water  used  in  the  pugging  of  shales  is  not  sufficient  to 
dissolve  or  loosen  all  of  the  cementing  salts  in  a  clay  even  by  continued 
pugging,  so  that  at  best,  only  a  portion  of  the  clay  particles  are  separated 
from  one  another,  but  the  manufacturers  must  continue* the  pugging 
until  a  sufficiently  large  number  of  grains  are  separated  to  form  a  slippery 
medium,  by  virtue  of  which  the  unslaked  or  undisintegrated  bundles  of 
particles  can  slip  past  one  another  freely  enough  to  permit  a  flowage  of 
the  mass  under  pressure.  The  difficulty  encountered  by  manufacturers 
in  breaking  down  the  cementing  bond  in  shales  is  increased  many-fold 
when  an  attempt  is  made  to  disintegrate  a  clay  into  its  ultimate  grains, 
as  is  done  in  mechanical  analysis.  The  data  for  texture  or  size  of  grain 
used  in  plotting  the  curves  in  Figs.  4  and  5  were  obtained  by  mechanical 
analysis  and  are  supposed  to  represent  the  subdivision  of  the  clays  into 
their  ultimate  particles.  While  it  is  comparatively  easy  to  obtain  separa- 
tion of  the  particles  in  loose-grained  clays  in  the  laboratory  and  in  the 
factory,  it  is  obvious  that  it  is  not  possible  to  obtain  a  similar  separation 
of  the  particles  of  the  hard  rock-like  clays  in  the  factory,  and  very  diffi- 
cult to  obtain  much  more  than  an  approximation  of  ultimate  subdivision 
in  the  laboratory.  It  is  owing  to  this  indefinite  degree  of  solution  of  the 
natural  bond  in  pugging  that  we  have,  in  the  case  of  shale .  bricks,  a  dis- 
cordant relation  between  the  porosity  of  the  brick  and  the  fineness  of 
grain,  shown  in  Figs.  2  and  5,  as  contrasted  with  the  semingly  concord- 
ant relation  in  the  case  of  the  loess  bricks,  as  shown  in  Fig.  4. 

Although  a  porosity  determination  on  a  green  brick  may  not.  be  of 
value  as  direct  evidence  of  the  so-called  "working  properties"  of  a  clay, 
it  can  be  shown  that  it  is  of  indirect  value,  in  that  the  data  can  be  used 
as  the  basis  of  many  interesting  and  valuable  calculations.  For  practical 
demonstration  of  the  commercial  possibilities,  or  exposition  of  the  work- 
ing properties  of  a  clay,  the  writer  has  failed  to  find  wherein  porosity 
data  on  unburned  bricks  separately  considered  are  of  use. 

Fineness  of  Grain. 

definition. 

By  fineness  of  grain  or  texture  of  a  clay  is  meant  the  size  of  its  min- 
eral particles.  Experimental  evidence  indicates  that  variation  in  grain 
controls  many  of  the  physical  and  pyro-chemical  properties  exhibited  by 
clays.  Plasticity,  shrinkage  in  drying  and  burning,  tensile  strength, 
drying  properties,  rate  of  oxidation,  rale  of  vitrification,  toughness  of 
burned  ware,  and  finally,  to  some  extent  pyrometric  value  of  the  clay, 
are  all  influenced  by  fineness  of  grain. 


150  PAVING   BRICK   AND    PAVING   BRICK   CLAYS.  [bull.  no.  9 

The  grains  of  many  clays  are  so  cemented  that  they  resist  separation 
in  the  ordinary  pug-mill  or  blunger.  When  two  or  more  particles  are 
thus  cemented  they  operate  as  a  unit  in  their  influence  upon  plasticity, 
tensile  strength,  drying  behavior,  etc.  This  accounts,  in  part,  for  many 
of  the  apparent  exceptions  to  the  general  rules  deduced  from  experiment- 
al evidence,  for,  in  the  usual  methods  applied  for  determining  fineness 
of  grain,  special  effort  is  made  to  separate  the  particles  completely. 
This  raises  the  question  whether  separation  of  the  particles  should  be 
carried  to  such  extremes  when  attempting  to  trace  direct  relations  be- 
tween fineness  of  grain  and  the  physical  properties  developed  in  the 
process  of  manufacture  of  clay  into  wares.  On  this  point,  however,  we 
have  no  direct  evidence,  except  perhaps  as  shown  in  Figs.  4  and  5,  so  the 
question  will  have  to  remain  unanswered  for  the  time  being. 

It  is  known,  however,  that  it  would  be  well-nigh  impossible  to  determ- 
ine how  far  a  mechanical  separation  of  the  particles  should  be  carried 
in  the  laboratory  to  make  the  test  comparable  to  the  separation  effected 
in  the  pug-mill,  wet  pan,  or  blunger.  For  this  reason  it  would  seem  as 
though  the  most  useful  data  concerning  texture  or  fineness  of  grain  can- 
not be  obtained  by  the  present  method  of  analysis. 

MEANS  OF  EXPRESSING  FINENESS  OF  GRAIN. 

If  all  the  particles  of  clay  were  considered  as  being  spheres  or  cubes 
their  superficial  areas  would  be  inversely  proportioned  to  their  diameters. 
*The  following  calculations  show  this  to  be  true  in  regard  to  the  sphere : 

D3 
Volume  of  a  sphere  is  equal  to  Pi  — ;  then  if  D  and  d  are  the  diameters 

6 

Pi  D3  Pi  d3 

of  two  spheres  their  volumes  would  be  proportional  as : 

6  6. 

The  number  of  spheres  required  to"  equal  in  volume  a  standard  unit 
PiD3  6  6 

volume  would  be  1  -= or  in  the  one  case,  and  in  the 

6  Pi  D3  Pi  d3 

other.  Since  the  surface  of  a  sphere  of  each  size  is  equal  respectively  to 
Pi  D2  and  Pi  d2  the  total  surface  area  of  a  collection  of  spheres,  having  a 

6  6 

total  volume  equal  to  unity,  would  be  in  each  case x  D2  and 

Pi  D3  Pi  d3 

6  6 

x  d2  or and respectively.     The  combined  areas  of  each  group 

Pi  D  Pi  d 

of  spheres  occupying  the  same  volume  but  having  different  diameters  are, 
therefore,  inversely  proportional  to  their  diameters.  This  proportional 
relation  of  the  surface  of  the  particles  in  the  several  groups  is  taken  as 
the  surface  factor  of  the  respective  groups,  and  the  sum  of  these  as  the 
surface  factor  of  the  clay. 

Cushman1  has  shown  the  error  involved  in  thus  taking  the  mean  of  the 
extreme  diameters  in  a  given  group.    According  to  data  given  by  Cush- 

1  Air  Elutriations  of  Fine  Powders,  Jour.  Am.  Chem.  Soc,  Vol.  XXIX,  No.  4,  p.  589, 
April  1907. 


purdy]  QUALITIES   OF   CLAYS    FOR    MAKING    PAVING   BRICKS. 


151 


man,  a  mechanical  analysis  of  the  separate  groups  would  show  a  predom- 
inance (77  to  87  per  cent  in  Cushman  data)  of  the  finer  particles  of  that 
group.  That  the  mean  diameter  obtained  as  described  above,  is  not  a  true 
mean  of  the  diameters  of  the  particles  in  a  group,  is  obvious.  The  error 
thus  involved  cannot,  however,  be  obviated  without  a  much  more  exten- 
sive subdivision  of  the  groups  than  is  possible  under  ordinary  conditions. 
It  needs  no  mathematical  demonstration  to  make  clear  that,  theoretically, 
the  more  extensive  the  analysis,  the  more  accurate  would  the  results  be. 
It  needs  but  a  short  experience  with  the  mechanical  analysis  by  any  of 
the  hydraulic  methods,  to  learn  that,  practically,  the  more  extensive  the 
analysis  is  made,  the  larger  will  be  the  operating  errors.  In  making  a 
mechanical  analysis  one  must  choose  between  the  Scylla  and  Charybdis  of 
these  errors  and,  naturally,  will  decide  in  favor  of  that  one  which  involves 
the  making  of  the  fewest  determinations. 

In  this  report  the  mean  of  the  extreme  diameters  of  each  group,  irre- 
spective of  the  distribution  by  number  according  to  their  volume,  of  the 
particles  within  the  respective  groups  is  taken  as  representing  the  diam- 
eter of  the  group.  The  mean  diameter  of  each  group  and  total  surface 
factors  for  the  clays  here  reported  are  shown  in  Table  V. 

VALUE  OF  DETERMINATION"  OF  FINENESS  OF  GRAIN. 

As  before  stated,  fineness  of  grain  is  the  probable  cause  of  several  of 
the  other  properties  exhibited  by  clays.  Since  fineness  of  grain  is  the 
cause,  and  the  other  properties,  in  a  large  sense,  the  effects,  the  true 
significance  of  this  determination  can  be  best  discussed  by  dealing  sep- 
arately with  the  properties  induced  by  size  of  grain. 

Numerical  Results. — In  Table  VII  is  given  the  per  centage  by  weight 
of  calcined  materials  in  each  of  the  several  groups  according  to  sizes  of 
particles. 

TABLE  VII. 


Sample  Number. 

Hygro- 
scopic 
water. 

Com- 
bined 
water. 

Percentage  Amount  by  Weight  of  Particles, 
Grouped  According  to  Diameters. 

Total. 

1M.  M. 

1-.1M.M. 

.1-.01. 

.01-. 001. 

.001-0.0 

K   1 

0.47 
1.03 
0.97 
1.68 
1.10 
0.70 
0.67 
1.20 
0.83 
1.74 
1.78 
1.48 
0.92 
0.66 
1.33 
1.10 
0.82 
1.35 
2.01 
1.69 
1.98 
1.63 
2.48 

5.73 
3.77 
6.90 
5.43 
5.60 
4.76 
5.46 
7.40 
3.32 
5.52 
8.32 
8.66 
6.13 
5.08 
7.69 
5.29 
6.11 
4.28 
4.35 
14.95 
11.97 
12.26 
7.71 

6.92 
0.96 
1.42 
1.30 
5.91 
1.14 
1.14 
8.76 

11.03 
0.85 
3.02 
3.64 
1.60 

13.66 
1.76 

10.92 
9.47 

12.67 
4.14 

12.14 
1.00 
0.19 
1.60 

6.19 
1.14 
1.47 
1.66 
1.04 
1.74 
3.42 
6.55 
1.49 
2.09 
2.69 
2.21 
0.79 
5.76 
5.90 
5.84 
2.54 
2.38 
3.62 
12.14 
1.86 
0.50 
2.56 

54.24 
63.75 
54.38 
46  47 
58.01 
63.17 
58.82 
45.95 
63.80 
22.96 
40.44 
38.03 
44.70 
41.24 
36.59 
50.67 
47.69 
50.78 
44.37 
24.57 
39.73 
22.50 
28.11 

22.92 
18.04 
23.03 
27.76 
21.04 
23.49 
24.45 
22.48 
13.79 
40.72 
33.76 
35.83 
38.80 
24.34 
36.23 
20.52 
26.78 
20.19 
25.24 
20.88 
29.73 
39.21 
38.20 

7.87 

13.33 

12.00 

19.34 

9.69 

7.62 

9.75 

8.26 

6.53 

23.93 

11.13 

12.13 

11.37 

8.14 

12.97 

9.93 

8.98 

12.80 

17.53 

17.60 

16.69 

26.39 

21.89 

104  36 

K   2 

102.04 

K   3 

100  18 

K   4 

104  68 

K   5 

102  41 

K   6 

102  65 

K   7  

103  73 

K   8 

100  61 

K   9 

100  83 

K10 

97  84 

Kll 

101  15 

K12 

102  00 

K13 

K14 

104  33^ 

98.91 

R    1 

102.49 

R    3 

R    4 

G-II 

104.30 
102.43 
104.48 

I-II 

H18 

101.30 
103.99 

H20 

102.79 

H21... 

102.71 

H23 

102  57 

152 


PAVING   BRICK   AND    PAVING    BRICK   CLAYS. 


[BULL.    NO.    9 


In  Table  VIII  will  be  found  the  same  data  with  the  hygroscopic  water 
eliminated  and  the  chemical  water  distributed  over  the  various  groups 
proportionally  to  the  amount  belonging  to  each,  as  determined  by  their 
loss  on  ignition. 

TABLE  VIII. 


Sample 
Number. 

•   1  mm 
mean 
diam. 
1.25. 

1mm 
mean 
diam. 
0.5. 

O.l-.Ol 
mean 
diam. 
0.05. 

.01-. 001 
mean 
diam. 
0.005. 

.001-0 
mean 
diam. 
0.0005. 

Total. 

Surface 
factor 

K    1 

7.27 
1.07 
1.50 
1.40 
6.38 
1.24 
1.35 
9.66 

11.39 
1.06 
5.36 
4.49 
1.82 

14.23 
2.16 

11.69 

10.15 
4.64 

13.05 
1.92 
0.34 
1.80 

13.17 

6.53 
1.23 
2.41 
1.74 
1.46 
1.83 
3.75 
6.90 
1.55 
2.42 
3.76 
2.88 
1.35 
6.31 
6.51 
6.30 
2.84 
3.81 
17.71 
2.75 
0.80 
2.86 
2.47 

56.07 
66.24 
57.15 
48.87 
60.57 
65.83 
60.87 
48.46 
65.50 
24.62 
43.74 
40.51 
46.74 
42.75 
38.70 
52.90 
49.32 
45.50 
27.57 
42.01 
24.34 
29.95 
52.57 

24.86 
19.63 
25.14 
29.41 
22.93 
25.98 
25.89 
25.40 
14.72 
44.29 
35.45 
38.82 
41.73 
26.03 
39.32 
21.60 
29.13 
25.94 
26.58 
32.47 
42.77 
40.82 
20.57 

9.76 
13.90 
13.96 
22.24 
11.43 

7.77 
11.81 
10.05 

7.63 
25.52 
12.94 
15.32 
13.15 

9.67 
15.53 
11.79 
10.85 
21.40 
19.22 
23.97 
34.62 
27.30 
15.72 

104.51 
102.09 
100.18 
103.68 
102.80 
102.66 
103.69 
100.50 
100.80 

97.91 
101.26 
102.04 
104.80 

98.99 
102.25 
104.29 
102.31 
101.31 
104.16 
103.13 
102.89 
102.74 
104.52 

256. 

K    2 

331. 

K    3 

341 

K    4    . 

514. 

K    5 

287. 

K    6 

221. 

K    7 

300. 

K    8 

262. 

K    9 

195. 

K  10 

604. 

Kll , 

339. 

K  12    . 

403. 

K13 

356. 

K14 

254. 

R    1 

397. 

R    3 

291. 

R    4    

275. 

I-II 

489. 

H  18 

444 

H20 

553. 

H21 

783. 

H23 

634. 

G    2     

366 

In  Table  IX  is  given  the  calculated  loss  on  ignition  of  each  group  as 
nearly  as  it  could  be  determined  from  the  results  of  analysis.  While 
this  loss  on  ignition  has  been  called  "Combined  Water/'  it  must  be  borne 
in  mind  that  the  loss  of  many  substances  other  than  combined  water 
has  been  included.  Carbon,  carbonic  acid,  sulphur,  etc.,  are  driven  off 
on  ignition  and  reduce  the  weight  of  the  sample.  The  relations  referred 
to  are  well  expressed  by  the  well-known  Kennedy  curves.     (See  Fig.  6.) 

Table  IX.    Distribution  of  combined  water  over  the  several  groups 

of  particles. 


Sample  Number. 

1  M.  M. 

1-.1M.  M. 

.1-.01 

.0— .001 

.001-0 

Total. 

K    1 

0.32 
0.09 
0.06 
0.07 
0.31 
0.09 
0.22 
0.82 
0.27 
0.19 
2.27 
0.80 
0.20 
0.48 
0.66 
0.60 
0.39 
0.40 
0.33 
0.79 
0.89 
0.16 

0.31 
0.08 
0.92 
0.05 
0.41 
0.08 
0.31 
0.30 
0.03 
0.28 
1.03 
0.63 
0.55 
0.33 
0.39 
0.27 
0.55 
0.17 
0.06 
5.45 
0.85 
0.23 

1.62 
1.85 
2.28 
1.66 
1.98 
2.22 
1.69 
2.01 
1.18 
1.24 
2.58 
1.95 
1.68 
1.26 
1.72 
1.45 
1.74 
0.24 
1.13 
2.76 
1.52 
1.13 

1.64 
1.37 
1.88 
1.25 
1.67 
2.33 
1.29 
2.69 
0.82 
2.83 
1.08 
2.49 
2.61 
1.54 
0.87 
2.13 
2.73 
0.19 
0.11 
5.49 
2.17 
1.67 

1.86 
0.43 
1.86 
2.69 
1.64 
0.09 
2.00 
1.71 
1.02 
1.15 
1.61 
3.02 
1.68 
1.48 
1.75 
1.80 
2.43 
3.51 
2.75 
1.44 
6.95 
4.89 

5  77 

K    2 

K    3 

3.84 
7  03 

K    4 

5  74 

K    5 

6  03 

K    6 

4  82 

K    7 

5  52 

K    8   

7  55 

K    9 

K10  

3.34 
5  71 

K  11 

8  58 

K  12 

8  91 

K  13 

6  74 

K  14 

5  11 

R    3     

5  40 

R     4 

6  27 

R     1 

7  87 

I    -1                           

4  53 

G  -2 

4  39 

H-18.     .               

15  95 

H-20 

12  41 

H-23 

8  11 

PURDY] 


QUALITIES   OF   CLAYS    FOR    MAKING    PAVING    BRICKS. 


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154  PAVING   BRICK   AND    PAVING   BEICK   CLAYS.  [bull.  no.  9 

The  distribution  of  "combined  water"  over  the  several  groups,  as  given 
in  Table  I,  was  necessarily  calculated  by  proportion,  for  the  total  loss 
on  ignition  of  the  finer  groups  in  some  cases  amounted  to  two  or  three 
times  that  which  occurred  on  ignition  of  the  whole  sample.  Satisfactory 
explanation  of  this  increase  or  gain  in  volatile  matter  during  the  process 
of  analysis  cannot  be  given.  It  is  supposed,  however,  that  it  is  due  in 
part  to  some  organic  growth  developed  in  the  water,  or,  possibly,  oil  from 
the  compressed  air  that  was  used  in  the  siphoning  oif  of  the  supernatant 
liquid.  That  this  last  suggestion  will  not  account  for  all  of  this  increase, 
if  any,  in  the  volatile  matter  accumulated  in  process  of  analysis,  was 
proved  by  the  fact  that  when  precautions  were  taken  to  clear  the  air 
of  all  possible  traces  of  solid  material,  there  was  still  nearly  the  same 
increase.  There  is  therefore  considerable  doubt  as  to  the  value  of  re-dis- 
tribution of  the  loss  on  ignition  by  means  of  proportions,  yet  the  data 
obtained  in  this  way  are  considerably  more  accurate  than  they  would 
otherwise  be. 

The  irregularities  in  the  data  are  pointed  out  solely  to  call  attention  to 
a  weak  point  in  this  most  important  determination.  Mechanical  analysis 
of  clays,  as  has  been  stated  before,  bids  fair  to  become  a  very  essential 
test  in  determining  the  full  value  of  a  clay,  and  attention  should  be  given 
to  the  elimination  of  this  increase  in  volatile  matter  during  the  process 
of  analysis.  Soil  physicists  are  experiencing  the  same  difficulty,  and  yet 
they  have  learned  to  give  considerable,  in  fact,  a  large  amount  of  credit 
to  the  mechanical  analysis  of  soils  as  a  means  of  determining  its  proper- 
ties for  their  purposes  . 

Shrinkage  in  Drying.    ■ 
methods  of  measurement. 

The  amount  that  a  clay  will  shrink  in  drying  is  expressed  in  per 
cents  of  the  unit  length  or  volume.  In  the  first  instance  the  shrinkage 
would  be  designated  as  linear  shrinkage,  and  in  the  second,  as  volume 
or  cubical  shrinkage. 

In  Table  I,  page  ?  ?,  will  be  found  the  percentages  of  both  linear  and 
volume  shrinkage  for  several  shale  clays  as  determined  by  direct  meas- 
urement. It  will  be  noted  that  the  variation  in  linear  shrinkage  in  60 
bricks  of  each  clay  is  far  in  excess  of  reasonable  limits.  When  the  linear 
shrinkage  varies  from  32  to  133  per  cent  from  the  average,  the  data  must 
be  wholly  unreliable.  In  presenting  this  data  it  is  felt  that  the  failure 
to  produce  more  consistent  results  lies  in  part  in  the  shortness  of  the 
shrinkage  distance,  and  in  part  in  carelessness  of  the  operator.  In 
marking  the  freshly  made  bricks  a  stencil  devised  by  J.  F.  Krehbiel  was 
used,  so  that  initially  the  shrinkage  lines  were  marked  upon  the  brick 
with  accuracy.  In  measuring  the  decrease  in  length  of  the  shrinkage 
line  after  the  bricks  were  dried,  a  vernier  shrinkage  scale  was  used  that 
read  accurately  to  the  third  place.  The  large  variations  in  the  results 
were  therefore  a  surprise  to  the  operator. 


purdy]  QUALITIES    OF   CLAYS    FOR    MAKING    PAVING    BRICKS. 


155 


The  volume  shrinkage  varied  within  fairly  reasonable  limits,  but  even 
here  the  variations  are  quite  large  considering  the  size  of  the  bricks  used. 
It  is  felt  that  if  in  one  case  the  variation  could  be  only  0.5  per  cent  there 
ought  not  to  be  any  excuse  for  a  variation  of  33.8  per  cent  in  another 
or  an  average  on  all  samples  of  11  per  cent. 

Inasmuch  as  the  volume  shrinkage  data  proved  to  be  the  more  accur- 
ate of  the  two  they  were  used  as  a  basis  on  which  to  calculate*  the  linear 
shrinkages  as  shown  in  the  following  table: 

Table  X.    Comparison  of  the  measured   with    calculated    linear 

shrinkage. 


Sample  No. 

Average 

volume 

shrinkage  in 

per  cents. 

Calculated 

linear 

shrinkage  in 

per  cents. 

Average 

measured 

linear 

shrinkage  in 

per  cents. 

Percentage 

variation 
on  volume 
shrinkage. 

Percentage 

variation 

in  measured 

linear 

shrinkage. 

K   1                

6.2 

12.2 

10.5 

10.1 

5.2 

10.1 

9.6 

7.5 

3.5 

18.3 

13.5 

12.7 

10.5 

6.1 

12.9 

13.1 

13.9 

9.1 

6.1 

11.5 

7.3 

14.3 

13.8 

14.4 

9.7 

7.8 

21.4 

16.5 

18.0 

20.4 

11.4 

2.1 
4.3 

3.6 
3.5 
1.8 
3.5 
3.3 
2.6 
1.2 
6.5 
4.7 
4.4 
3.6 
2.1 
4  5 
4.6 
4.9 
3.1 
2.1 
4.0 
2.5 
5.0 
4.8 
5.1 
3.4 
2.7 
7.7 
5.8 
6.4 
7.3 
4.0 

1.5 
3.5 
2.1 
3.3 
1.6 
4.1 
3.9 
2.1 
0.9 
5.8 
3.3 
3.6 
3.3 
1.5 
2.7 
4.2 
4.5 
3.3 
3.2 
5.0 
1.9 
5.5 
4.2 
4.6 
3.7 
2.8 
7.0 
6.8 
7.2 
7.4 
4  0 

33.8 

2.4 

16.7 

5.8 

6.7 

10.3 

12.2 

21.5 

34.1 

0.5 

16.3 

5.9 

7.5 

11.5 

19.0 

10.6 

5;7 

25.3 
6.7 
7.8 

12.5 
7.6 
2.9 
4.1 
6.8 

19.6 
4.6 
3.0 
1.7 
5.8 

10.5 

133.3 

K  2 

70.0 

K  3 

68.0 

K    4 

73.6 

K    5 

129  0 

K   6 

43.9 

K   7 

K   8 

51  2 
95.2 

K   9 

75.0 

K10 

37  8 

Kll 

73  8 

K12 

44.4 

K13 

48.4 

K14 

93.3 

S     1 

S     2 

60.0 
42.8 

R    1 

R    2 

R    4 

53.3 
36.3 
56.2 

B  II 

32.0 

C  II 

124.0 

H  II 

65.4 

I    II 

J    II 

33.3 
34.7 

L  II 

54  0 

H  16.     . 

78  5 

H  17 

34.2 

H  20 

26.5 

H  21 

41.6 

43.2 

H  24. 

45.0 

*  If  a  unit  cube  shrinks  so  that  each  edge  is  decreased  by  linear  length  "a" 
then  the  new  length  of  the  edges  become  (1-a).  If  the  decrease  in  volume 
of  this  same  cube  be  represented  by  "x"  then  the  new  volume  will  be  (1-x). 
Since  the  edges  of  the  cube  are  now  (1-a)  its  volume  can  also  be  represented 

by  (1-a) 3  hence  (1-a) 3  is  equal  to  (1-x),  or  a=l-Vl-x.     It  was  by  this  form- 
ula that  the  transformation  from  volume  to  linear  shrinkages  were  made. 


156 


PAVING   BRICK   AND    PAVING   BRICK   CLAYS. 


[BULL.    NO.    9 


The  linear  shrinkage  which  probably  is  the  more  correct  for  that 
sample  is  underscored.  In  cases  where  there  is  not  an  underscored  linear 
shrinkage,  there  is  no  possible  way  to  judge  which  one  is  the  most  correct. 
In  case  the  calculated  practically  agrees  with  the  measured  linear  shrink- 
age, both  are  underscored. 

If  the  volume  and  linear  shrinkages  had  been  correctly  measured,  there 
would  have  been  no  discrepancy  between  the  calculated  and  determined 
linear  data.  If  any  importance  at  all  is  to  be  attached  to  shrinkage  data 
it  is  evident  that  extreme  care  should  be  exercised  in  their  determination. 
When  possible,  the  measured  linear  should  be  checked  by  calculation 
from  the  volume  shrinkage  and  vice  versa. 

RELATION  OF  VOLUME  SHRINKAGE  TO  POROSITY. 

It  will  be  noted  from  a  glance  at  Fig.  7  that  there  does  not  seem  to  be 
any  relation  whatever  between  volume  shrinkage  and  pore  space  in  the 
dried  bricks. 

Fig.  8  also  represents  the  same  sort  of  irregular  relation  between  the 
volume  shrinkage  and  pore  space  in  the  dried  brick  made  from  the  Iowa 
loess  clays.1 

RELATION  OF  VOLUME  SHRINKAGE  TO   WATER  OF  PLASTICITY. 

The  chart,  (Fig.  9),  showing  the  relation  between  the  percentage  of 
water  of  plasticity  and  the  volume  shrinkage  from  the  green  to  the 
dried  condition,  proves  that  while  there  is  some  indication  of  a  reciprocal 
relation  between  these  two  factors,  this  relation  cannot  be  affirmed. 


a* 


oHir 

o  H23 

II 210 

0 

KlOO 
11 00 

Rio 

OH/ 
OK12 

oh-11 

oKll 

Si 

o.J-U 

oS2 

OHM 

fiffi 

>   o  L-ll 

oB-II 

Kio 
o 
me 

oA'/i 

OK  6 
K7 

OC-JJ 

oKS 

oKli       < 
QK5 

>K1 

SK9 

16  13  20  22 

PERCENT  POROSITY  OF  GREEN  BRICK 

Fig.  7.  Diagram  showing  relations  between  volume  shrinkage  and  'porosity  of  dried  brick. 

(From  data  in  Table  I.) 


1  la.  Geol.  Surv.,Vol.  XIV,  1904,  p.  109  and  113. 


PURDY] 


QUALITIES   OF   CLAYS    FOR    MAKING   PAVING    BRICKS. 


157 


RELATION  OF  VOLUME  SHRINKAGE  TO  WATER  IN  EXCESS  OF  THAT  REQUIRED 

TO  FILL  THE  PORES. 

It  would  seem  that  if  the  volume  had  been  determined  at  regular  in- 
tervals as  the  bricks  lost  their  mechanical  water  by  evaporation,  the  per 
centage  up  to  the  time  that  the  brick  reached  its  maximum  shrinkage, 


28 
26 
24 
22 

I10 

S  18 

St    16 

s 

*3  14 

i* 

& 

*  10 

1 
g « 

6 
4 

<">* 

or, 

024 

OlS 

19< 

> 

2?0 

no 

031 

HO 

032 

02 

QlO 

07 

°9 

022 

OiK 

012 

°26 

020 

40 

°15 
0?3 

( 

>30 

08 

Ol8 

021 

029  ( 

>5 

< 

>i 

< 

>25 

280 

i 

~>14 

1 

7          1 

S         1 

9         2 

■)          2 

1         2 

2         2 

3         2 

4          2 

5          2 

5          2 

7         2 

8         2 

9         3 

?         31 

PERCENT  POROSITY 

Fig.  8.  Diagram  showing  relation  between  volume  shrinkage  and  porosity  of  loess  clays 
from  Iowa.    (After  Beyer  and  Williams.) 

would  stand  in  closer  relation  to  the  volume  shrinkage  than  does  the  total 
mechanical  water  and  volume  shrinkage.  It  is  not  known  what  value 
such  a  test  would  have,  but  it  would  probably  be  considerably  more  than 
is  the  determination  of  total  mechanical  water  alone. 

In  Table  XI  is  shown  the  percentage  by  weight  of  water  that  would 
be  required  to  fill  the  pores  of  bricks  made  from  Iowa  clays  and  that 
which  is  in  excess  of  the  "pore  water."  These  clays  were  ground  until 
they  would  pass  through  a  40-mesh  sieve/  then  wetted  with  water  and 
thoroughly  wedged.  Grinding  the  clay  until  it  would  pass  a  40-mesh 
sieve  would  reduce  the  size  of  the  larger  grains,  and  to  some  extent  break 
down  bunches  of  grains  by  force  that  would  not  have  been  affected  by 
the  water  used  in  wedging.  The  data  is  of  interest  on  this  account  in 
connection  with  the  problem  of  shrinkage. 


Ia.  Geol.  Surv..Vol.XIV,1904,p.  76. 


158  PAVING    BRICK    AND    PAVING    BRICK   CLAYS.  [bull.  no.  9 

TABLE  XL 


Clay. 


Per  cent 
Water. 


Porosity 


Sp.  Gr. 


Vol.  of 

clay 
per  100. 


Per  cent 

by  wt.  of 

water  in 

pores. 


Per  cent 

by  wt.  of 

clay. 


Excess 
water  for 

plas- 
ticity. 


Flint   Brick   Co..    top 

stratum 

Flint  Brick  Co.,  middle... 
Flint  Brick  Co.,  bottom. .. 
Flint  Brick  Co.,   green 

brick 

Iowa    Brick  Co.,    top 

stratum 

Iowa  Brick  Co.,    second 

from  top 

Iowa  Brick  Co.,  third 

from  top 

Iowa  Brick  Co.,   fourth 

from  top 

Iowa  Brick    Co.,   fifth 

from  top 

Iowa   Brick  Co.,     bottoir. 

stratum 

Cap.C.  Brick  &  P.   Co.. 

top  stratum 

Cap.  C.  Brick  &  P.  Co., 

second  from  top 

Cap.  C.  Brick  &  P.  Co., 

third  from  top 

Cap.  C.  Brick  &  P.  Co., 

fourth  from  top 

Jester  Clay  Bank 

Harris  Brick  Yard 

Dale  Brick  Co.,  top  loess.. 
Dale    Brick    Co.,    bottom 

shale 

Corey  P.  B.  Co.,  red  burn- 
ing clay 

Corey  P.  B.    Co.,  buff 

burning  clay 

Colesburg  

Morm  Lake  B.  &  T.  Co  . .. 
Besley  Brick    Yard,    top 

loess 

Besley  Brick  Yard,  middle 

loess 

Besley    Brick  Yard,    bot- 
tom loess 

Getham   Bros.,    inland 

loess 

Cap.   City  B     &  P.  Co., 

bottom  stratum 

Cap.  City  B.   &   P.    Co., 

green  brick 

Granite  B.  Co.,   top 

stratum 

Granite    B.   Co.,    lower 

stratum 

Clermont  B.  &T.  Co 
Am.  B.  &T.  Co 


22.5 
25.0 
25.0 

17.31 
23.00 
30.04 

25.0 

23.20 

17.5 

17.43 

25.0 

25.73 

27.5 

29.57 

25.0 

17.96 

25.0 

26.04 

27.5 

28.69 

30.0 

30.80 

22  5 

25.25 

22.5 

17.00 

22.5 
20.0 
22.5 
22.5 

25.13 
20.35 
24.33 
18.14 

22.5 

28.98 

25.0 

30.10 

25  0 

27.5 
25.0 

28.10 
28.36 
19.27 

22.5 

29.77 

22.5 

25.30 

22.5 

24.03 

25.0 

22.43 

22. 

24.59 

22.5 

21.83 

22.5 

23.06 

22.5 

20.0 
30.0 

22.41 

22.66 
26.71 

2.41 
2.51 
2.40 

2.52 

2.53 

2.46 

2.40 

2.45 

2.37 

2.36 

2.69 

2.48 

2.53 

2.45 
2.49 
2.56 
2.44 

2.48 

2.54 

2.54 
2.62 
2.42 

2.34 

2.32 

2.40 

2.41 

2.40 

2.51 

2.25 

2.42 

2.58 
2.51 


77.00 
69.96 

76.80 

82.57 

74.27 

70.43 

82.04 

73.96 

71.31 

69.20 

74.75 

83.00 

74.87 
79.65 
75.67 
81.86 

71.02 

69.90 

71.90 
71.64 
80.72 

70.23 

74.70 

75.97 

77.57 

75.41 

88.17 

76.94 

77.59 
77.34 
73.29 


7.99 
10.64 
15.83 

10.71 

7.52 

12.92 

15.32 

8.20 

12.93 

14.76 

14.43 

11.44 

7.49 

12.04 
9.30 

11.15 
8.32 

14.13 

14.49 

12.86 

13.12 

8  97 

15.34 

12.73 

11.64 

10.71 

11.96 

8.97 

11.75 

10.51 
10.10 
12.67 


92.01 
89.36 

84.87 

86.29 

92.48 

87.08 

84.68 

91.80 

87.07 

85.24 

85.57 

88.56 

92.51 

87.96 
90.70 
89.85 
91.68 

85.87 

85.51 

87.14 

86.88 
91.03 

84.66 

87.27 

88.36 

89.29 

88.04 

91.03 

88.25 

89.49 
89.90 
87.33 


14.51 
14.36 
9.87 

14.29 


12.07 

12.18 

17.80 

12.08 

12.74 

15.57 

11.06 

15.01 

10.46 
10.70 
11.35 
14.18 

8.87 

10.51 

12.14 
14.38 
16.03 

7.16 

9.77 

10.86 

14.29 

10.54 

13.53 

10.75 

11.99 
9.90 
17.33 


In  making  Table  XI  Byers'  and  Williams  figures  for  porosity,*  specific 
gravityf  and  water  of  plasticityj  .were  taken,  and  the  data  calculated  as 
follows : 

If  porosity,  or  volume  of  pore  space,  is  29.77  per  cent  in  a  unit  volume 
there  would  be  0.2977  parts  by  volume  of  pore  space,  and  1.0000 — 0.2977 
or  0.7023  volumes  of  clay.  On  the  assumption  that  the  pore  space  is 
filled  with  water  and  the  specific  gravity  of  the  clay  is  2.31,  there  would  be 


*Ia.  Geol.  Surv.,Vol.  XIV,  1904.    flbid  116    $Ibid  83. 


PURDYj 


QUALITIES   OF   CLAYS   FOR    MAKING    PAVING    BRICKS. 


159 


0.2977X1-00=0.2977  parts  by  weight  of  water,  and 
0.7023X2.34=1.6434  parts  by  weight  of  clay,  or  ex- 
pressed as  per  cents — 15.3  and  84.6  per  cent  respectively  of  water  and 
clay.  This  15.3  per  cent  of  water  then  is  the  amount  of  water  by  weight 
that  would  be  required  to  fill  the  pore  spaces  in  a  brick  that  would  weigh 
100  at  the  time  when  all  the  particles  have  become  fixed  or  arranged  in 
the  exact  position  that  they  will  maintain  during  the  remainder  of  the 
drying  period.  This,  it  is  assumed,  would  give  the  weight  of  water  that 
remains  in  the  pores  of  the  bricks  at  the  time  the  clay  "has  reached  its 


8" 

o 

&• 

as 


Kl2 
o 


0H24 


OR2 


O  O 

oK5 


oK9 


Kn 
o 


oK8 
OKI 


°U17 


H210 


OJ-JI 

H-Il 


_Q_^i_ 


L'll 


oB-n 


OH16 


Kioo 

OH20 


12  U  16  18 

PERCENT  A  GE  WA  TER  OF  PLASTICITY 


H23Q 


Hl7o 


22 


Fig.  9.  Diagram  showing-  relation  between  amount  of  water  required  to  develope  plasticity 
and  volume  shrinkage.    (Data  from  Table  I.) 

maximum  air  shrinkage.  This  amount  of  water  subtracted  from  the 
amount  required  to  develop  plasticity  would  give,  if  the  foregoing  as- 
sumption is  correct,  the  amount,  the  amount  of  water  required  to  lubri- 
cate the  particles  sufficiently  to  cause  a  state  of  mobility  which  we  have 
learned  to  designate  as  plasticity. 

Fig.  10  shows  that  there  is  some  reciprocal  relation  between  the  amount 
of  water  in  excess  of  that  required  to  fill  the  pores  of  a  dried  brick,  (as 
given  in  Table  XI)   and  the  volume  shrinkage. 

In  Table  XII  are  shown  the  calculations  on  the  Illinois  clays,  designed 
to  bring  out  the  same  facts  given  in  Table  XL  In  this  table,  however, 
the  amount  of  hygroscopic  water  is  given  in  each  case  so  that  it  can  be 
reckoned  in  as  part  of  the  mechanical  water,  if  so  desired.  It  must  be 
borne  in  mind,  however,  that  the  amount  of  water  calculated  as  being 
in  excess  of  that  required  for  filling  the  pores  does  not  in  any  way  include 
the  hygroscopic  water.     The  hygroscopic  water  is  not  added  in  with  the 


160 


PAVING    BRICK   AND    PAVING    BRICK   CLAYS. 


[BULL.   NO.    9 


SB 


24 


as 


/» 


?U      ^°0l 


012 
55 


T 


015/ 
/ 

/ 


,'ou 

0  29 


C22 


OU 


013 


610 


04 


07 


&3 


123 


d$rfli 


Q21 


26    " 
O    O 


OH 


-4  6  8  10  12  14  U  If) 

PERCENT  BY  WEIGHT  OF  WATER  IN  EXCESS  OF  THAT  REQUIRED  TO  FILL  POKES 


•Fig.  10.  Diagram  showing  relation  of  volume  shrinkage  to  water  in  excess  of  that  required  to 

fill  the  pores  in  Iowa  clays. 


TABLE  XII. 


Sample 
Number. 

Plasticity 
water. 

Porosity. 

Sp.  Gr. 
by  pyc- 
nometer. 

Per  cent 
by  weight 

of  water 
required  to 

fill  the 
pores. 

Excess 
water  re- 
quired for 
plasticity. 

Hygro- 
scopic 
water. 

Vol. 
shrinkage. 

K-l 

14.9- 

16.77 

16.82 

16.27 

13.06 

17.03 

17.57 

14.4 

13.4 

19.6 

13.35 

16.3 

13.6 

17.2 

16.6 

13  4 
13.0 
13.2 
17.7 
11.8 
16.5 

14  4 
16  5 
16.4 
16  2 
16.6 
18.3 
18.0 
21.4 
12.8 

26.0 
25.7 
25.6 
27.8 

25  4 
28.9 
27.9 
25.2 
26.1 
25.4 
18.3 
28.3 
24.5 
23.0 
26.4 
17.8 
24.0 
21.8- 

26  9 
22.4 
20.7 
18.9 
24.2 
24.5 
27.8 
19.0 
23.9 
21.6 
24.9 
14.5 

2.67 
2.56 
2.69 
2.67 
2.65 
2  66 
2.64 
2.69 
2.70 
2.69 
2.67 
2.70 
2.64 
2.64 
2  72 
2.73 
2  72 
2.72 
2.67 
2.70 
2.68 
2.67 
2.70 
2.70 
2.70 
2.60 
2.72 
2.72 
2.63 
2,66 

11.6 
11.9 
11.4 
12.6 
11.3 
13.2 
12.7 
11.1 
11.5 
11.2 

7.7 
12  7 
10.9 
10.1 
11.6 

7.9 
10.4 

9.3 
12.1 

9.6 

8.8 

8.0 
10.5 
10.7 
12.4 

8.2 
10.3 

9.2 
11.1 

5.9 

3.3 
4.8 
5.4 
3.6 
1.8 
3.8 
4.9 
3.3 
1.9 
8  4 
5.7 
3.6 
2.5 
7.1 
5  0 
5.5 
2.6 
3.9 
5.6 
2.2 
7.7 
6.4 
6.0 
5.7 
3.8 
8.4 
8.0 
7.8 
10  3 
6.9 

2.01 
1.62 
2.43 

6.2 

K-2 

12.2 

K- 3 

10.45 

K-4 

10.12 

K-5 

0.923 

1.23 

1.93 

1.70 

0.79 

2.31 

5.09 

2.16 

0.79 

4.76 

2.42 

1  95 
.   1.53 

2.28 
1.67 
1.14 
3.07 
2.85 

2  70 
3.05 
1.74 
3.7 
2.58 
3.98 
2.05 
1.63 

5.17 

K-  6 

10.6 

K-7 

9.62 

K-8    

7.51 

K-9 

3.54 

K-10 

18.29 

K-12  . . . 

12.74 

K-13 

10.54 

K-14 

6.13 

S-  1 

11.97 

S-   2 

13.1 

R-  1 

13.9 

R-  2 

9.1 

R-4 

5.98 

B-II     

11.5 

G-II 

7.32 

H-II 

14.3 

I-II  

13.8 

J-II  

14.4 

L-II 

9.7 

H-16 

7.8 

H-17 

21.4 

H-20 

16.5 

H-21 

18.0 

H-23 

20.4 

H-24 

*  11.4 

PURDY] 


QUALITIES   OF   CLAYS    FOR    MAKING    PAVING    BRICK. 


161 


water  of  plasticity,  because  there  is  some  doubt  as  to  just  where  and  how 
the  clay  retains  that  water  on  drying.  It  is  supposed  to  be  held  either  in 
or  between  the  grains,  and  does  not  greatly  exceed  the  amount  (on  ac- 
count of  the  natural  humidity  of  the  air)  that  the  powdered  clay  would 
retain  as  moisture. 

The  porosity  data  used  are  those  given  in  Table  I. 

In  the  above  table  there  is  the  same  indication  of  a  reciprocal  relation 
between  the  "excess  water"  and  volume  shrinkage  as  noted  in  the  case 
of  the  Iowa  clays  and  shown  in  Fig.  11.  We  have  here  then  the  promise 
of  a  means  of  obtaining  analytically  a  line  on  the  drying  behavior  of  a 
clay  other  than  volume  shrinkage  taken  alone. 


is 


K4 


366.4 
OGIJ 


pKl4 


286.8 


195.3j9/ 


k. 


355.9 
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OR2 


261.7  < 


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bKl  275.3 


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397.2 


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330 


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300.3 
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11 


VH21     A 

7823         ' 


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2  4  6  8  M  12 

EXCESS  WA  TER  PLCS  HYGROSCOPIC  WATER 


T4 


Fig.  11— Diagram  showing  relation  of  volume  shrinkage  to  water  in  excess  of  that  required  to 

fill  the  pores  in  Illinois  clays. 

—11  G 


162 


PAVING   BRICK   AND    PAVING   BRICK   CLAYS. 


[bull.  no.  9 


RELATION  OF  VOLUME  SHRINKAGE  TO  FINENESS  OF  GRAIN. 

The  volume  shrinkage  of  a  clay  is  a  reliable  index  of  its  drying  be- 
havior only  within  certain  limits.  Take  for  instance  K — 14  and  H — 17, 
which  lie  close  to  the  extremes  of  minimum  and  maximum  volume 
shrinkage;  both  require  considerable  care  in  drying.     Roughly  we  can 


M 

/ 

/ 

/kio 

16 

u 

12 

id 

g 

/ 

/ 

»       / 

/ 

c 

OKU 

OK2 

Hi         /0 

r 

oKi2< 

/ 

nK6 

**>*"/ 

/ 

1 

oA'J 

< 

/ 

6 

0K8 
/ 

/           OG-ll 

r 
/  is 

■i 

/ 

K!> 

100  200  300  400  oOO  600  700 

SURFACE  FACTOR 

Fig.  12.  Diagram  showing  relation  of  volume  shrinkage  Lo  fineness  of  grain. 

say  that  clays  which  exhibit  an  average  shrinkage  will  dry  safely,  and 
that  if  the  ware  exhibits  either  a  high  or  low  volume  shrinkage  it  can 
be  assumed  to  be  likely  to  occasion  trouble  in  drying.  But  knowing  this 
general  fact,  how  can  the  drying  behavior  of  a  particular  clay  be  esti- 
mated ? 

It  has  been  suggested  that  clays  which  have  a  fair  range  in  size  of 
grain,  i.  e.,  not  too  large  a  proportion  of  either  the  largest  or  smallest 
grains,  can  be  dried  with  greatest  safety.     This  we  proved  to  be  true  for 


PURDY]  QUALITIES   OF   CLAYS    FOR    MAKING    PAVING    BRICK.  163 

the  clays  plotted  near  the  middle  of  a  diagonally  drawn  dotted  line  in 
Fig.  L2  were  the  easiest  to  dry  and  those  at  the  extreme  ends  the  most 
difficult. 

It  was  demonstrated,  however,  that  while  there  may  possibly  be  a 
reciprocal  relation  between  porosity  and  fineness  of  grain  in  the  naturally 
soft  and  loose-grained  clays,  there  is  no  trace  of  such  a  reciprocal  rela- 
tion in  the  harder  clays,  like  shales,  because  the  cement  which  holds  the 
grains  is  not  broken  by  the  methods  of  preparation  usually  employed. 
It  has  also  been  shown  that  there  is  no  reciprocal  or  proportional  rela- 
tion between  the  porosity  of  the  dried  ware  and  the  volume  of  shrinkage. 
This  same  lack  of  proportional  relations  was  found  between  water  oi; 
plasticity  and  volume  shrinkage,  as  well  as  water  of  plasticity  and  por- 
osity. The  only  factors  that  seem  to  exhibit  any  proportional  relation 
with  volume  shrinkage  are  "excess  water"  and  fineness  of  grain.  These 
factors  alone  are  not,  however,  sufficient  evidence  on  which  to  base  an 
answer  to  our  query. 

Tensile  Strength, 
methods  of  testing. 

One  of  the  vital  factors  affecting  the  drying  behavior  of  clays  is  their 
cohesion.  Many  ways  have  been  devised  to  measure  this  cohesion,  but 
the  tensile  strength  test  seems  to  be  the  most  popular.  Determinations 
of  tensile  strength  as  usually  made  and  reported,  have  so  large  a  per- 
centage of  variation  that  they  are  practically  worthless.  This  has  been 
justly  attributed  to  the  personal  factors  entering  into  the  preparation  of 
the  test  pieces.  It  is  indeed  surprising  how  variable  the  results  can  be 
even  when  the  operator  uses  all  the  care  possible  in  wedging  the  clay 
and  pressing  the  briquette.  The  personal  factors  have  been  largely 
eliminated  in  the  tests  here  reported  by  following  a  method  for  making 
briquettes  devised  by  H.  B.  Fox,  of  the  University  of  Illinois. 

Fox  Method. — The  Fox  method  is,  in  the  main,  as  follows :  The  clay 
is  mixed  with  just  sufficient  water  to  make  a  thick  paste.  It  is  allowed  to 
stand  in  this  condition  for  some  time,  generally  twelve  or  more  hours, 
and  is  then  poured  onto  a  slightly  moistened  plaster  slab  and  allowed  to 
harden  until  it  has  assumed  about  the  consistency  of  "stiff  mud."  It  is 
then  cut  into  briquettes  by  a  cutter  similar  to  a  biscuit  cutter.  The  clay 
is  forced  out  of  this  cutter  into  the  briquette  mold  by  a  plunger  under 
a  given  load;  in  our  case  about  50  pounds.  While  the  load  is  still  on, 
the  cutter  is  removed  and  the  briquette  struck  off  with  a  wire.  By  this 
means  the  briquette  is  formed  and  pressed  under  uniform  conditions 
without  the  introduction  of  personal  factors,  with  the  possible  exception 
of  the  making  up  of  the  slip. 

The  briquettes  are  then  room-dried.  In  this,  care  is  exercised,  for 
the  fine-grained  clays  and  the  exceptionally  weak  clays  can  be  dried  so 
fast  as  to  cause  them  to  "dry  check."  It  is  not  always  possible  to  see 
these  "dry  checks,"  but  there  is  no  doubt  that  a  considerable  proportion 


164 


PAVING   BRICK   AND    PAVING   BRICK   CLAYS.  [bull.  no.  9 


<j    a 


!   V^3 


yr\:/-m\-Y/////M 


purdy]  QUALITIES   OF   CLAYS   FOR   MAKING   PAVING   BRICK.  165 

The  briquettes  are  then  grooved  to  a  slight  depth  by  the  use  of  a  file 
operated  in  a  miter,2  making  a  uniform  cross  section  in  all  cases.  The 
object  of  this  grooving  is  not  to  obtain  a  uniform  cross  section  primarily, 
but  to  insure  the  breaking  of  the  briquette  at  the  narrowest  section.  Be- 
ing uniform,  the  cross  section  can  be  considered  as  a  constant  factor,  thus 
making  easier  the  calculation  of  the  results.  This  grooving  was  not 
trusted  to  give  us  a  constant  cross  section,  however,  but  each  briquette 
was  measured  with  a  vernier  shrinkage  scale  that  reads  to  three  places. 

The  results  of  grooving  the  briquettes  may  be  noted  in  the  table  given 
below.  There  it  will  be  seen  that  the  strength  per  square  centimeter 
cross  section  is  not  materially  different.  In  fact  the  only  difference  in 
strength  between  the  grooved  and  the  ungrooved  can -be  said  to  be  within 
the  limits  of  errors  that  are  unavoidable  in  this  test.  The  usual  contrast 
between  the  variation  in  results  in  the  grooved  and  in  the  ungrooved 
briquettes  which  ordinarily  exists  cannot  be  seen  in  the  result  given  be- 
low. The  results  are  exceptionally  good  in  all  cases,  irregular  results 
due  to  breaking  elsewhere  than  at  the  neck  not  being  reported. 

After  the  briquettes  are  grooved  they  are  made  bone  dry  in  a  hot  air- 
bath  and  cooled  in  a  dessicator  so  as  to  eliminate  all  moisture,  and  then 
broken  in  a  Fairbanks  Tensil  Strength  Machine. 

Wedging  Versus  Slip  Process. — Clay  workers,  especially  the  old  potters 
who  make  large  jars  by  "throwing"  on  a  wheel,  recognize  a  difference  in 
the  working  properties  of  clay  when  prepared  by  the  slip  process  and 
when  prepared  by  the  "chaser,"  wet  pan,  or  the  old-time  stamping  pro- 
cess. In  fact  the  difference  in  the  clay  when  prepared  in  slip,  or  in  one 
of  the  "plastic"  methods,  is  so  marked,  that  where  ware  is  to  be  thrown 
the}-  install  special  machinery  on  which  to  prepare  the  clay,  and  in  one 
of  the  most  up-to-date  terra-cotta  factories  in  the  west,  they  keep  four 
men  tramping  the  wet  clay  with  their  bare  feet,  in  preference  to  using 
the  cheaper  slip  method.  In  the  manufacture  of  glass  pots,  tramping 
with  bare  feet  is  the  method  most  generally  used  in  preparing  the  clay. 
For  this  reason  the  fairness  to  all  clays  in  casting  the  slab  from  which 
the  briquettes  were  cut  was  questioned,  and  the  following  tests  were 
made  to  throw  light  on  this  point. 

All  the  clays  for  both  the  "slip"  and  "wedge"  process  were  made  to 
pass  through  a  10-mesh  sieve. 

The  clay  for  slip  process  was  cast  as  in  the  Fox  method. 

The  clay  for  the  wedge  process  was  thoroughly  wedged  by  hand  while 
at  its  state  of  maximum  plasticity,  and  then  worked  into  a  sheet  1V2" 
thick  on  the  plaster  slab  -by  pounding  it  with  a  flat  board.  Briquettes 
were  cut  and  forced  into  the  mold  under  constant  pressure  as  in  the 
case  of  the  slip  clay. 

The  results  are  shown  in  Table  XIII : 


See  Fig.  13. 


166 


PAVING    BRICK    AND    PAVING    BRICK   CLAYS. 
TABLE  XIII. 


[BULL.   NO.    9 


Sample. 

Slip  Process 

average 
strength  in 
lbs.  per  sq. 

CM. 

Per  Cent 
Variations 
Using  Aver- 
age 
Strength 
as  Basis. 

Wedge 
Process. 

average 
strength  in 
lbs.  per  sq. 

CM. 

Per  Cent 
Variations 
Using  Aver- 
age 
Strength 
as  Basis. 

0 

o 
o 

<! 

n 
p. 

<3o 

o  <-•■ 

o 

< 

a 

O 

o 

o 
< 

o  <-•• 

o 
< 
n 

0 

3 
0 

6 
a 

o  <-•' 

o 

ri 
p- 

Q 
*i 

o 

0 

a> 
a 

3  - 
o 
< 
a 

a 

K— 14  Western  Brick  Co.,  Dan- 
ville, 111 

16.20 
29.80 
17.65 
17.85 
8.25 
16.85 

17.60 
33.30 
20.40 
21.90 
9.25 
18.60 

9.9 
10.3 
10.3 
13.3 
8.5 
5.37 

4.5 
11.9 

8.8 

13.0 

8.05 

4.0 

28.9 
36.8 
23.9 
24.0 
9.3 
21.7 

18.00 
31.6 
23.9 
24.3 
9.9 
22.1 

6.9 
17.1 
16.7 
37.5 

3.35 
14.3 

12  2 

K— 10  Terre  Haute,  Ind 

K— 3  Albion,  111 

25.3 
18  4 

K— 11   Brazil  shale,  Ind 

K— 9  Crawfordsville,  Ind 

K— 8  Veedersburg,  Ind 

30.0 
11.1 
21.2 

17.60 

20.17 

9.61 

8.37 

24.1 

21.60 

15.97 

16  3 

The  following  conclusions  were  reached  as  a  result  of  these  tests: 

First — In  every  case  except  that  of  the  Terre  Haute  not  grooved,  the 
wedging  process  gave  higher  results. 

Second — The  variation  is  considerably  lower  in  the  slip  than  in  the 
wedge  process. 

Third — The  increased  strength  due  to  wedging  was  not  sufficient  to 
warrant  the  accompanying  increase  in  percentage  of  variation. 

Fourth — Grooving  the  briquettes  did  not  materially  better  the  results 
in  the  slip  process  and  actually  made  the  results  worse  in  the  wedge 
process.  It  must  be  remembered  in  this  connection,  however,  that  the 
results  of  briquettes  that  did  not  break  at  the  necks  were  rejected.  All 
grooved  briquettes  broke  at  the  neck. 

Fifth — Grooving  increased  the  variation  in  coarse  non-plastic  clays, 
such  as  K — 14  and  K — 9,  but  did  not  seem  to  effect  the  finer  grained 
clays. 

Effect  of  fine  Grinding — In  view  of  the  fact  that  grooving  aids  ma- 
terially in  reducing  the  variation  in  all,  except  the  less  plastic,  coarse 
grained  clays,  it  was  thought  that  perhaps  the  comparison  would  be 
more  just  if  all  were  finely  ground. 

The  dry-pan  samples  of  the  two  plastic  clays,  K — 10  and  K — 11, 
and  the  two  coarse  and  less  plastic  clays,  K — 14  and  K — 9,  were  ground 
of  the  variations  are  due  to  them. 

wet  and  also  dry  until  they  passed  through  sieves  of  10,  20,  40  and  80 
mesh,  as  follows : 

A  quantity  of  clay  sufficient  to  make  six  briquettes  was  taken  from 
the  stock  by  quartering,  making  ample  allowance  for  waste.  This 
sample  was  first  crushed  to  pass  a  10-mesh  sieve.     It  was  then  sieved 


purdy]  QUALITIES   OF   CLAYS   FOR    MAKING    PAVING   BRICK.  167 

through  the  desired  mesh  and  the  residue  placed  in  a  small  Bonnot  mill 
with  100  Iceland  pebbles.  Both  the  wet  and  the  dry  samples  were 
taken  from  the  mill  every  five  minutes,  and  the  particles  fine  enough 
to  pass  through  the  desired  mesh  were  sieved  out.  The  residue  left  on 
the  sieve  was  then  placed  in  the  mill  and  ground  for  another  five 
minutes.  This  grinding  was  continued  until  all  the  clay  passed  through 
the  desired  mesh.  In  this  manner  there  was  prepared,  by  both  wet  and 
dry  grinding,  stocks  that  would  just  pass  the  10,  20,  40  and  80  mesK 
sieves. 

The  clays  that  were  ground  were  kept  at  casting  consistency,  i.  e., 
quite  thick  slush,  so  that  when  completely  ground  they  were  cast  into 
slabs  as  quickly  as  convenient.  The  clays  prepared  by  the  dry  method 
were  allowed  to  stand  in  water  until  they  assumed  the  thick  slip  state 
and  then  cast  on  plaster  of  Paris  slabs  after  standing  from  10  to  21' 
hours. 

Briquettes  were  cut  and  pressed  by  the  Fox  method.  In  table  XIV 
will  be  found  the  results  of  this  experiment. 

The  work  was  done  by  a  man  not  accustomed  to  it  who  could  not  at 
first  be  made  to  realize  the  importance  of  taking  the  greatest  pains  to  in- 
sure constant  conditions  and  accurate  results.  This  may  account  for  the 
higher  variations. 

From  these  results  the  following  conclusions  may  be  drawn: 

First — The  variations  with  the  grooved  briquettes  are  on  the  whole 
lower  than  those  with  the  ungrooved. 

Second — The  average  strength  of  the  grooved  is  practically  equal  to 
that  of  the  ungrooved. 

■Second — The  average  strength  of  the  grooved  is  practically  equal  to 
that  of  the  ungrooved. 

Third — Finer  grinding  either  wet  or  dry  does  not  materially  better 
the  constancy  of  the  results.  The  fact  is,  in  this  experiment,  the  varia- 
tions in  the  finer  ground  samples  were  higher  in  many  cases  than  in 
the  coarsely  ground  samples. 

Fourth— The  average  strength  of  the  clay  was  not  materially  altered 
by  finer  grinding. 

Fifth — The  results  by  wet  grinding  differed  but  little,  if  any,  from 
those  by  dry  grinding. 


PAVING    BRICK   AND    PAVING   BRICK   CLAYS.  [bull.  no.  9 


Per  cent  variation 
ungrooved  ... 


Per  cent  variation 
grooved  


SO 

fcH  03 

O 

w 
« 


Grinding  duration 
in  minimum 


Per  cent  variation 
ungrooved  


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PURDY] 


QUALITIES   OF   CLAYS   FOR    MAKING    PAYING   BRICK. 


169 


RESULTS    OF   TESTS. 


In  the  light  of  the  foregoing  tests  it  was  decided  to  dry-grind  the 
clays  in  a  jaw  crusher  to  pass  a  20-mesh  sieve.  In  this  the  whole  sam- 
ple, including  the  fine  and  coarse  particles,  was  passed  through  the 
jaw  crusher.  Six  briquettes  were  made  by  the  slip  method,  as  designed 
by  Fox,  and  grooved  to  insure  breakage  at  the  neck.     In  this  manner 


the  following  data  was  obtained: 


TABLE  XV. 
Tensile  Strength  of  Clays. 


Strength  in  kilograms 
per  sq.  cm. 

Percent  of  Var- 
iation. 

Sample. 

Maxi- 
mum. 

Mini- 
mum. 

As 
tested. 

By  elimi- 
nation 
of 

irregular- 
ities. 

K—  1  Alton,  111 

7.356 

12.292 

9.934 

10.806 

5.715 

8.164 

6.985 

5.359 

4.373 

13.245 

9.525 

12.971 

8.346 

6.713 

6.124 

6.033 

7.212 

8.210 

9.163 

23.406 

8.664 

11.114 

9.662 

5.216 

5.359 

10.251 

10.513 

9  753 

9.254 

14.469 

13.742 

10.069 

8.925 

12.111 

7.168 
8.437 
8.074 
8.664 
5.216 
7.516 
5.896 
4  717 
3.773 

11.762 
8.664 

12.201 
6.713 
5.359 
5.629 
5.307 
8  942 
5.806 
7.666 

15.558 
.    7.503 
8.936 
7.393 
4.717 
4.717 
7.892 
9.252 
8  664 
8.014 

13.880 

12.383 
9.662 
8.028 

10.523 

7.58 

31.52 

18.72 

18.8 
8.73 
7.202 

15.62 

11.9 

13.7 
5.508 
9  03 
6.78 

19.5 

20.1 
8.08 

12.03 

12  5 

29.2 

16.3 

37.8 

13.4 

19.6 

23.4 
9.56 
7.97 

23.00 

11.9- 

11.1 

13.4 
4.4 
7.04 
8.09 

10.0 

13.1 

K—  2  Hydraulic,  St.  Louis.  Mo 

K—  3  Albion  ,111 

6  84 

K— 4  Springfield,  111 

11  1 

K—  6  Galesburg,  111 

K—  7  Streator  Paving  Brick  Co 

K —  8  Veedersburg,  Ind 

K—  9  Crawfordsville,  Ind 

K— 10  Terre  Haute,  Ind 

K— 11  Brazil,  Ind  

K— 12  Hrazil  Fire  Clay 

K— 13  Clinton,  Ind 

K— 14  Western  Brick  Co.,  Danville,  111 

14.9 

K— 15  Barr  Clav  Co.,  Streator,   111 

H— 16  Carter,  Peoria 

H— 18  Sterling.  Ill 

H— 20  Savanna,  111 

H— 21  Galena,  111 

H— 23  Carbon  Cliff,  shale 

H— 24  Carbon  Cliff '  fire  clay 

R—  1  Nelsonville,  Ohio 

R—  2  Portsmouth,  Ohio 

6.93 

R —  3  Canton '  Ohio,  Imperial  plant 

R —  4  CantonOhio,  Royal  plant  . 

S—  1  Moberly,  Mo 

S—  2  Kansas  City,  Mo 

B — II  Atchison,  Kan 

G— II  Coffeyville,  Kan  

H— II  Topeka,  Kan 

I  — II  Caney.   Kan 

J— II  Pittsburg,   Kan 

L — II  Lawrence.  Kan 

F  —  1  Danville  Brick  Co 

CAUSE  FOR  VARIATION   OF  MORE  THAN    15   PER  CENT. 

K-2.  There  were  two  briquettes  that  broke  with  high  strength  and  two 
with  low  strength. 

K-3.  There  was  one  briquette  that  broke  with  low  strength.  By  throw- 
ing out  that  briquette  the  variation  would  be  reduced  to  6.84. 

K-4.  There  was  one  briquette  that  broke  with  high  strength.  By  throw- 
ing out  that  briquette  the  variation  was  reduced  to  11.1. 

K-7.     There  were  two  briquettes  that  broke  with  low  strength. 

K-13.     There  were  two  briquettes  that  broke  with  low  strength. 

K-14.  There  was  one  briquette  that  broke  with  low  strength.  Elimination 
of  this  briquette  would  make  the  variation  14.9. 


170 


PAVING   BRICK   AND    PAVING   BRICK   CLAYS. 


[BULL.   NO.    9" 


H-20.  There  was  one  briquette  that  broke  with  high  and  another  with 
low  strength. 

H123.  .  There  was  one  briquette  that  broke  with  high  and  another  with 
low  strength. 

R-l.  There  was  one  briquette  that  broke  with  low  strength.  Elimination 
of  this  briquette  would  make  the  percentage  only  6.93. 

R-2.  Three  of  these  briquettes  broke  with  high  and  three  with  low 
strength. 

S-l.  There  was  one  briquette  that  broke  with  high  and  one  with  low 
strength. 

The  results  here  reported  are  exceptionally  good.  The  variation  in 
the  strength  of  dry  clay,  as  made  by  other  methods,  usually  runs  from 
25  to  50  per  cent  in  nearly  every  reported  instance.  In  fact,  it  is 
.seldom,  if  ever,  that  a  report  on  tensile  strength  will  show  a  lower 
variation  than  25  per  cent.  The  placing  of  15  per  cent  as  the  maxi- 
mum variation  to  be  allowed  would  be  very  severe  standard  ordinarily, 
but  the  general  character  of  the  work  as  here  reported  justifies  the  limit. 

RELATION    OF    TENSILE    STRENGTH    TO    FINENESS    OF    GRAIN. 

Curves  were  plotted  from  data  given  by  Eies1,  and  also  by  Beyer  and 
Williams2,  showing  the  relation  between  fineness  of  grain,  as  delineated 
by  the  surface  factor,  and  tensile  strength.  There  did  not  appear  to  be 
any  consistent  relation  between  these  two  factors,  shown  by  the  curves. 


700 
600 
500 

I 

KlOrV 

/ 
/ 

on 20 

0 

/ 

/K4 

H°18 

/ 
/ 

/ 

OJ-JI 

OK12 

8 

I 

<*     '00 

■- 

/ 
/      K3 

oGZ 

1  *&n 

200 
100 

R4o  ^ / 

Ah 

/ 

oKl 
oK6 

/ 

yk.9 

2  4  6  8  10 

TENSILE  STRENGTH  IN  KG.  PER  SQ.  CM 

Fig.  14.  Diagram  showing  relation  between  tensile  strength  and  fineness  of  grain. 

Notwithstanding  the  apparent  contradiction  in  the  case  of  the  New 
Jersey  and  Iowa  clays,  it  is  believed  that  fineness  of  grain  in  a  given 
clay  does  bear  a  relation  to  the  tensile  strength.  Orton1  has  shown  the 
influence  of  different  sized  grains  upon  a  very  close  grained  and  tough 

1  New  Jersey  Geological  Survey,  Vol,  6,  p.  89. 

2  Iowa  Geological  Survey,  Vol.  X(V,  p.  84. 
1  Trans.  Amer.Cer.Soc,  Vol. Ill,  p. 117. 


PURDY]  QUALITIES   OF   CLAYS    FOR    MAKING    PAVING    BRICK.  171 

ball  clay.  This  clay  is  so  fine  by  itself  that  it  is  extremely  difficult  to 
dry  without  air  checking,  but  with  Increasing  adulteration  of  sand  up 
to  30  per  cent  by  weight,  the  tensile  strength  increased  up  to  a  maxi- 
mum in  the  sample  where  the  sand  was  of  extreme  fineness,  and  here 
again  the  tensile  strength  decreased  rapidly.  This  drop  in  the  curve  is 
credited  to  the  inability  of  the  extremely  fine  mixture  to  part  with  its. 
mechanical  water  without  checking,  thus  causing  flaws  in  the  briquette 
and  very  materially  weakening  it.  In  this  experiment  we  have  at 
both  extremes  very  fine  grained  materials;  one  a  pure  ball  clay  and  the 
other  the  same  ball  clay  adulterated  by  fifty  per  cent  by  weight  of  a 
very  fine  sand,  both  having  a  low  tensile  strength.  The  intermediate 
members  of  this  series  show  increasing  strength  with  decrease  of  size 
of  grain.  So  far  at  least  as  this  one  case  is  concerned,  increase  in  size 
of  grain  increases  tensile  strength.  Fineness  of  grain  and  tensile 
strength  are,  therefore,  functions  of  one  another. 

We  know  that  a  fine-grained  shale  is,  in  a  majority  of  cases,  im- 
proved by  adulteration  with  sandstone,  even  in  the  fact  of  the  fact 
that  the  sandstone  is  very  coarse.  At  Streator,  111.,  there  are  two  strata 
of  shale  in  one  bank,  the  one,  being  very  gritty,  is  easily  manufactured 
into  a  good  paver;  the  other,  a  close  grained  plastic  shale,  gives  trouble 
in  every  stage  of  manufacture,  and  makes  a  poor  paver.  Yet  these 
two  shales  are  said  to  be  of  very  similar  chemical  composition.  The 
writer  believes  that  the  cause  of  this  difference  does  not  lie  in  their 
chemical  composition,  shrinkage,  or  ability  to  slake  easily,  but  in  their 
drying  behavior.  Judging  from  the  results  of  Prof.  Orton's  experi- 
ment on  the  tough  ball  clay,  it  is  believed  that  if  many  of  the  plastic, 
fine  grained  clays  were  by  addition  of  coarse  material  opened  suffi- 
ciently to  permit  ready  egress  of  the  mechanical  water,  they  would  be 
excellent  paving  brick  material1,  while  without  such  a  treatment  they 
would  be  worthless  for  anything  other  than  building  brick,  simply  be- 
cause the  bond  of  the  clay  would  be  weakened  in  drying  by  the  expand- 
ing steam  inside  of  the  brick  which  could  not  readily  escape. 

In  Fig.  14  data  are  plotted  showing  the  relation  between  fineness  of 
grain  and  tensile  strength.     This  is  indicated  by  the  dotted  line. 
It  will  be  noted  that  there  is  a  'general  relation  between  fineness  of 
grain  and  tensile  strength.     This  is  indicated  by  the  dotted  line. 

There  is  a  remarkable  coincidence  in  the  relative  positions  of  the 
several  clays  in  Fig.  14  and  Fig.  11.  The  same  relative  positions  of  the 
several  clays  is  to  be  seen  also  in  Fig.  12  which  shows  the  relation  be- 
tween volume  shrinkage  and  surface  factor.  This  same  relative  posi- 
tion of  the  clays,  one  with  another,  was  developed  also  when  the  rela- 
tion between  the  sum  of  the  excess  and  hygroscopic  water  and  the  surface 
factor,  and  also  the  relation  between  the  sum  of  the  excess  and  hygro- 
scopic water  and  the  tensile  strength,  were  plotted.  In  the  last  two  in- 
stances, however,  the  order  in  which  the  clays  occurred  was  the  reverse 
of  that  in  Fig.  14  and  11. 

1  It  is  not  desired  that  the  reader  should  infer  that  this  is  suggested  as  a  panacea  for  all 
clays  or  that  all  clays  can  be  "doctored"  so  as  even  theroetically  to  make  them  fit  tor  paving 
brick  manufacture. 


172 


PAVING   BRICK   AND    PAVING   BRICK   CLAYS. 


[BULL.   NO.    9 


RELATION   OP   TENSILE  STRENGTH   TO   VOLUME   SHRINKAGE. 

We  have  seen  that  there  is  a  greater  shrinkage  of  the  mass  when  dried 
from  stiff  mud  to  bone  dryness,  as  the  grains  of  the  clay  decrease  in 
size.  If  these  fine  particles  are  composed  largely  of  clay  substance  they 
will  possess  a  degree  of  cohesion  that  will  cause  the  dried  mass  to  become 
quite  hard,  the  hardness  increasing  directly  with  increase  of  cohesion 
possessed  by  the  individual  particles.    With  increase  of  exposed  surface, 


is 


16 


3=1  m 


K9Q 


OK8 


KjJcu 


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7 

oKd 


L 


K130 

Kud 


OK7 


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()S16 


oki 


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OH20 


"Ml 


KJlO 


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OB-Il 


V 


oo-fi 


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4  6  8  W 

TENSILE  STRENC  TH  JN  KC  PER  SQ.  CM. 


OK10 


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/- 


OH-I1 


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OK12 


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fm 


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Fig.  15.  Diagram  showing  relation  between  volume  shrinkage  and  tensile  strength. 

ought  to  be  an  increase  in  tensile  strength,  for  the  closer  the  particles 
are  to  one  another  the  greater  will  be  the  bond  between  them.  De- 
crease in  size  of  grain,  increase  in  volume  shrinkage  and  increase  in  ten- 
sile  strength   should,   therefore,   follow   one 


another   in   this   order   as 


purdy]  QUALITIES   OF   CLAYS   FOR    MAKING   PAVING   BRICK.  173 

causes  and  effects.     Such  a  relation  is  shown  in  Fig.  15  where  the  vol- 
ume shrinkage  and  tensile  strength  are  plotted  coordinately. 

The  drying  behavier  of  a  given  clay  then  can  be  said  to  be  a  function 
of  four  factors  acting  simultaneously,  viz :  Volume  shrinkage,  excess 
water,  fineness  of  grain  and  tensile  strength.  The  greater  the  volume 
shrinkage  and  the  larger  amount  of  excess  water  present,  the  more  dan- 
ger will  there  be  in  drying.  The  greater  the  fineness  of  grain  and  the 
larger  the  tensile  strength,  the  safer  ought  the  clay  to  dry,  all  other 
things  being  equal.  If  a  drying  modulus  were  to  be  formulated  it  would 
have  in  the  numerator  the  surface  factor  (S),  representing  the  fineness 
of  grain,  and  tensile  strength  (T)  ;  in  the  denominator  there  would  be 
the  percentage  of  volume  shrinkage  (1)  and  excess  water  (E),  that  is, 
S    T 

This  simple  relation  is  not,  however,  expressive  of  the  true  rela- 

V   E. 

tive  value  of  the  involved  factors.     It  is  believed  that  the  formula. 

S3  T 

V3  E    approximates  th^  truth  more  closely. 

100 

Plasticity, 
theories  of  plasticity. 

There  is  probably  no  property  of  unburned  clay  which  has  been  more 
widely  discussed  than  plasticity.  To  plasticity  the  clay  owes  its  re- 
sponsiveness to  every  touch  of  the  potter's  hand  and  its  adaptability 
to  the  preservation  of  every  line  of  the  artist's  tool ;  it  is  this  quality  that 
permits  of  its  being  drawn  out  into  sheets  and  cylinders  of  the  most 
astonishing  thinness. 

Of  the  many  theories  advanced  as  to  the  cause  of  plasticity  the  fol- 
lowing are  the  most  tenable: 

Molecular  Attraction  Theory — To  properly  appreciate  this  conception 
of  the  cause  for  plasticity,  suppose  clay  to  be  blunged  into  the  form  of 
a  slip,  as  is  the  practice  of  the  potter  before  casting  a  vase.  In  this 
slip  or  fluid  condition  each  grain  is  surrounded  Or  enveloped  by  a  film 
of  water.  If  the  volume  of  water  is  large  compared  with  the  total  vol- 
ume of  clay  particles,  the  mass  will  behave  in  every  respect  like  a 
fluid;  indeed,  as  will  the  turbid  water  of  the  Mississippi.  Suppose  that, 
by  evaporation,  or  adsorption  by  a  plaster  mold,  the  volume  of  the 
water  be  decreased.  The  clay  particles  will  be  brought  closer  and  closer 
to  one  another,  causing  the  mass  to  pass  from  a  fluid  state  through  var- 
ious stages  of  consistency  until  it  assumes  a  stiff  plastic  condition ;  a 
process  to  be  observed  in  mud  roads  after  every  rain.  When  in  this 
stiff  condition  the  particles  still  have  an  envelope  of  water  or,  in  other 


174  PAVING    BRICK    AND    PAVING    BRICK   CLAYS.  [bull.  no.  9 

words,  they  are  still  suspended  in  water  just  as  truly  as  they  were  when 
the  mass  was  more  of  a  fluid.  But,  owing  to  their  proximity,  it  is 
assumed  by  those  advancing  this  theory  of  plasticity,  that  they  are  held 
in  position  by  the  molecular  attraction  which  each  particle  of  clay  sub- 
stance exerts  on  the  other. 

Molecular  attraction  is  a  known  force,  and  there  has  been  no  adequate 
proof  advanced  upon  which  positive  claims  can  be  made  against  such  a 
force  operating  between  clay  particles  when  brought  into  close  proxi- 
mity. The  popular  conception  of  a  bar  of  iron  is  that  it  is  a  rigid 
homogeneous  mass,  but,  as  is  shown  in  magnetization  experiments,  it 
is  made  up  of  individual  particles  which  can  be  turned  about  or  set  up 
endwise,  thus  acting  independently  of  one  another  except  in  the  matter 
of  the  molecular  attraction  that  each  exerts  upon  its  neighbor,  binding 
or  holding  the  whole  together.  Aside  from  composition  the  degree  of 
molecular  attraction  determines  the  hardness  of  the  iron.  Iron,  then, 
is  a  solid  fluid,  that  is,  it  will  flow.  The  force  of  gravity  is  not  sufficient 
to  overcome  this  molecular  attraction  and  cause  flowage,  but  when  a 
force  that  exceeds  that  of  the  molecular  attraction  is  applied,  flowage 
follows  in  the  direction  of  the  greater  force.  It  is  in  this  respect  that 
iron  is  a  fluid. 

If  similar  flowage  is  attempted  when  the  grains  in  a  clay  mass  are 
practically  dry,  or,  in  other  words,  not  surrounded  by  water,  except  per- 
haps that  held  by  absorption,  pressure  sufficient  to  overcome  the  force 
binding  or  holding  the  particles  together  will  disrupt  the  ware.  That  is, 
instead  of  flowage  of  the  particles  in  this  comparatively  dry  state,  rup- 
ture is  a  possibility.  Further,  maximum  plasticity  or  ability  to  flow  i§ 
not  attained  until  the  maximum  number  of  particles  is  enveloped  with 
the  least  amount  of  the  suspending  medium.  This  same  phenomenon  is 
to  be  noted  with  almost  all  fine  insoluble  powders,  Wheeler1  has  shown, 
for  instance,  that  the  non-plastic  slates,  Iceland  spar,  propyllite,  gypsum 
and  halloysite  can  be  made  to  develope  a  much  smaller  but  still  a  fair 
degree  of  apparent  plasticity  with  water  as  a  floating  medium.  When 
dried,  the  force  required  to  disrupt  these  masses,  while  small,  is  yet 
comparatively  great.  The  difference,  however,  between  the  behavior  of 
clay  and  these  finely  pulverized  minerals  is  that  the  latter  can  be  molded 
by  pressure  alone  into  a  shape  that  will  have  a  comparatively  higher 
tensile  strength  than  if  they  were  caused  to  acquire  that  shape  by 
flowage  due  only  to  assumed  plasticity.  But  we  know  that  maximum 
density  and  consequent  strength  can  be  best  developed  in  plastic  clay 
by  the  combined  influence  of  pressure  and  plasticity.  I\rowT  is  it  mole- 
cular attraction  in  the  case  of  clay,  as  in  that  of  iron  which  can  be  bent, 
stretched,  rolled,  etc.,  in  the  cold  without  rupture,  or  is  it  merely  that 
clay  grains  may  be  pressed  so  close  together  that  flowage  is  permitted 
so  long  as  water  is  present  in  excess,  but  is  resisted  by  fractional  force 
when  dry? 

>Mo.  Geol.  Surv.,Vol.  XI.  p.  106. 
2Carhart,  H.S., Univ. Physics, Pt.  I. 


PURDYj  QUALITIES   OF   CLAYS   FOR    MAKING   PAVING   BRICK.  175 

Text  books  on  physics  give  as  an  "expression"2  for  the  force  of  mole- 
cular attraction  between  two  molecules,  M  and  M',  MM'f  (r).  "All  that 
is  known  about  this  funtion  of  r  is  that  it  is  very  large  for  insensible 
distances,  that  it  diminishes  very  rapidly  as  r  increases  and  that  it 
vanishes  while  r  is  still  very  small.  The  maximum  value  of  r  at  which, 
molecular  action  ceases  is  estimated  by  Quincke  to  the  0.00005  mm;' 
If  the  particles  then  were  0.00005  mm.  or  0.00002  inches  apart,  they 
would  be  at  the  extreme  distance  through  which  molecular  attraction 
can  possibly  operate.  Grout1  says,  however,  "Now  a  simple  calculation, 
based  on  the  mechanical  analysis  of  the  clays,  will  show  that  the  amount 
of  water  needed  to  place  a  film  0.00005  mm.  thick  around  each  grain 
is  often  nearly  equal  to  the  amount  added  in  tempering,  so  that  in 
ordinary  plastic  clay,  it  is  necessary  to  consider  practically  all  the  water 
as  being  under  this  influence." 

Grout2  bases  his  reasoning  on  the  following  calculations:  He  found 
that  his  "mechanical  analyses  frequently  show  a  large  percentage  of 
grains  below  0.001  mm.  in  diameter,  also  from  0.001  to  0.005  mm. 
The  average  diameter  of  grains  below  0.001  mm.  is  0.0005  mm.  If 
these  are  considered  spherical  and  of  specific  gravity  2.5,  it  would  re- 
quire 25.5  per  cent  by  weight  of  water  to  place  around  each  grain  a 
film  0.00005  mm.  thick." 

On  making  these  same  calculations  the  following  was  obtained: 

PiD3 

•Vol.  of  sphere= 

6 
Given  diameter  of  sphere  0.00005 

Pi  — 

Log  —  =     1.71899 

6         8         — 
Log   0.0005    ==    10.09691 
11.81590  =  Log    6545X10-14      volume      of      clay 

sphere. 
Diameter    of   sphere    plus    water    film  =  .0005  + 
.0001  or  .0006 
Pi  — 

Log    —         =     1.71899 
6 

3       10.33445 

Log       .0006= ■— 

10.05344  =  Log    1131  XS  10-is    vol- 
ume   in    cu.    mm.     of 
sphere     of    clay    plus 
water. 
Reducing  these  figures  for  the  sake  of  convenience  to 

0.6545  =  volume  of  clay  sphere, 
1.131    =  volume  of  clay  plus  water  sphere. 
0.6545-^1.131  =  0.5775,   part   of    unit   volume   of 
clay  plus  water  sphere 
occupied  by  the  clay. 
1.00     —.5776  =  0.4224,   part  occupied   by  water 
film. 


lJour.Am.Chem.Soc.,Vol.XXVII,No.9,Sept.l905. 
JLoc.cit.,p.l046. 


176  PAVING   BRICK   AND    PAVING   BRICK   CLAYS.  [bull.  no.  9 

Given  specific  gravity  of  clay  =  2.5 

Since  in  the  metric  system  Vol.  X  Sp.  Gr..=Weight 

0.5775      X      2.5=1.4540    parts  by  weight  of  clay 
0.4224      X      1.0=  .4224    parts  by  weight  of  water 


1.8764    total  weight. 
0.42246  -M.8764  =  0.2251,    parts    by    weight    of 

water  in  a  unit  vol- 
ume of  clay  plus 
water  film,  or  22.5 
per  cent. 

This  calculation,  so  far  as  the  validity  of  Grout's  argument  is  con- 
cerned, checks  his  results. 

Grout  further  calculated  that  if  this  same  volume  of  clay  were  con- 
sidered as  a  square  plate  one-fifth  as  thick  as  wide,  instead  of  a  sphere, 
over  54  per  cent  of  water  would  be  held  to  the  clay  particles  by  this- 
molecular  attraction.  Supposing  it  to  be  fair,  inasmuch  as  the-kaolin- 
ite  crystal  is  "plate-like,"  to  consider  that  in  a  clay  half  of  the  grains 
are  approximately  spherical  and  the  remainder  plate-like.  Grout  fig- 
ures that  a  clay  having  all  its  particles  the  size  here  assumed  would  take 
by  virtue  of  the  molecular  attraction  of  the  clay  particles,  40  per  cent 
of  water. 

In  a  personal  interview  the  writer  suggested  to  him  that  he  was 
taking  the  maximum  limit  of  the  distance  through  which  this  molecular 
attraction  can  be  said  to  operate.  His  defense  was  that  when  the 
spheres  were  devoid  of  a  water  film  they  touched  one  another,  but  as 
they  gathered  to  themselves  this  water  film,  they  need  not  necessarily 
be  separated  .00005  mm.,  for  the  film  crowded  from  the  points  of  closest 
proximity  could  be  considered  as  filling  up  the  space  that  would  other- 
wise have  to  be  considered  as  void. 

It  must  be  admitted  by  the  supporters  of  Grout's  molecular  attraction 
theory  for  plasticity,  that  he  used  but  a  portion  of  a  very  fine-grained 
clay  on  which  to  calculate  his  demonstrating  example.  If  he  had  taken 
into  consideration  the  data  for  the"  sample  of  clay  as  published  by  him 
instead  of  only  those  for  the  finer  portions,  quite  different  results  would 
have  been  obtained  as  is  shown  in  Table  XVI. 

The  calculations  by  which  the  data  in  the  following  table  were  ob- 
tained are, 

(a)     Volume  of  clay  sphere  PiDs  where  D   is  the  mean   diameter  of  the 

range  in  each  group  of  the  mechanical 

6      analysis. 

Pi   (D  — 0.0001)3  — PiD3 

(6)     Volume  and  weight  of  water  film  

6  6 

(c)  Weight  of  dry  clay  particles  as  given  in  the  mechanical  analysis. 

(d)  Total  or  collective  volume  of  spheres  in  each  group:  Weight  given 
—  Sp.  Gr.  of  the  clay. 

(e)  Number  of  spheres  in  each  group  per  unit  volume:   Total  volume  of 

d 
each  group  -t-  volume  of  clay  sphere  or  — 

a 


PURDY] 


QUALITIES    OF   CLAYS    FOR    MAKING    PAVING    BRICK. 


177 


(f)  Weight  of  water  film  surrounding  the  sphere  in  each  group  of  the 
sample:  Weight  of  water  film  times  the  number  of  spheres  or  e  X  b. 

(g)  Sum  of  water  required  to  give  each  particle  in  the  sample  a  water 
film  of  prescribed  thickness. 

TABLE  XVI. 


Sample. 

Sp.  Gr. 

Total  dry 

weight  of 
clav  par- 
ticles by 
analysis. 

Total 
weight  of 
water  films 

by 
calculation 

Analyst. 

Reference  to  data 

used  and  explanatory 

notes. 

S.  C.  Besley,  top  clay  (1) 
S.  C.  Besley,  middle  clay 
S.  C.  Besley,  bottom  clay 

Dale  Brick  Co 

2.34 
2.32 
2.40 

2.44 
2.41 
2.52 

2.35 

2.66 

2.58 

2.66 

2.56 

2.686 

2.67 

2.65 

2.66 

2.636 

2.689 
2.702 

2.69 
2.659 
2.669 
2.71 

2.72 
2.73 
2.66 

2.72 

0.9844 
0.9834 
0.9819 

0.9857 
0.9739 
0.9880 

0.9870 

0.987 
0.984 
1.045 

1.021 

1.002 
1.037 
1.028 
1.027 
1.037 

1.005 
1.008 

0.979 
1.013 
1.021 
1.048 

0.9899 

1.023 

1.043 

1.023 

0.0165 
0.0219 
0.0263 

0.0320 

0.00254 

0.0393 

0.1750 

0.1009 

0.1043 

0.0356 

0.0491 
0.0475 
0.0703 
0.0390 
0.0320 
0.045 

0.036 
0.029 

0.0804 
0.0467 
0.0533 

0.0479 

0.0348 
0.0519 
0.041 

0.03902 

W     iams. 

..do 

..do... 

..do 

pp.  116  and  123,  la.  Geol. 
Surv.,  Vol.  XIV. 

Williams'  first  group  was 
termed"aboveO,l  MM." 

In  this   group  the  mean 
diameter  of  the  particles 
was  assumed  to  be  O. 
175  M.  M. 

.  .do . . . . 

Clarksburg  fire  clay  (2)... 

Bridgeport  stoneware 
clay  (2)  

Grout 

..do 

..do 

..do 

Krehbiel 
and  Moore 

pp.  65 and  251  W.Va.  Geol. 
Surv.,  Vol.  III. 

pp.  65  and  162  W.Va.  Geol. 

Charleston  river  clay  (3) . 
Parkersburg  pottery  clay 
K-l    Alton,  111.  (4) 

Surv.,  Vol.  III.  Attract- 
ed water=  15  -f  per  cent. 

pp.65  and  200  W.Va.  Geol. 
Sury.,  Vol.  III. 

pp.65  and  160 W.Va.  Geol. 
Surv.,  Vol.  III. 

K-2    St.  Louis  Mo 

K-3    Albion,  111 

K-4    Springfield,  111 

K-5    Edwardsville,  111... 

t 

K-6    Galesburg,  111 

K-7    Streator.  B.pB.  Co.. 

Krehbiel 
and  Moore 

Calculated 
by  Merry. . 

K-8    Veedersburg,    Ind. 

K-9    Crawfordsville.Ind. 

K-10  Terre  Haute,  Ind. .. 

K-ll  Brazil  shale.  . . 

K-12  Brazil  fire  clay 

No.  2.  fire  clay. 

K-13  Clinton,  Ind 

K-U  Western   P.   B.  C, 
Danville 

R-l    Nelsonville,  O 

No.  2  fire  Clay. 

R-3    Canton,  O.  (Imper- 

ial)   

R-4    Canton, O.  (Royal). 

—12  G 


178 


PAVING   BRICK    AND    PAVING    BRICK   CLAYS. 


[BULL.   NO.    9 


Table  XVI—  Concluded. 


Sample. 

Sp.Gr. 

Total  dry 
weight  of 
clay  partic- 
les by 
analysis. 

Total 
weight  of 
water  films 

by 
calculation 

Analyst. 

Reference  to  data  used 
and  explanatory  notes. 

Ill    Caney,  Kan 

2.67 
2.71 
2.67 
2.72 
2.72 

2.63 

1.013 
1.045 
1.042 
1.031 
1.029 

1.027 

0.0670 
0.0463 
0.0593 
0.0739 
0.10301 

0.0867 

G-ll  Coffey ville,  Kan... 

H-18  Sterling,  111 

J3-20  Savanna,  111...;.... 

H-21  Galena,  111 

H-23  Carbon    Cliff,    111. 
(shale) 

(1)  The  Iowa  clays  are  loess. 

(2)  Stoneware  or  No.  2  fire  clays. 

(3)  Alluvial  clay. 

(4)  The  Illinois  clays  are  shales  in  every  instance  except  K-12  and  R-l. 

In  Table  XVI  there  is  but  one  instance  that  of  the  West  Virginia 
stoneware  clay,  in  which  the  amount  of  water  molecularly  attracted  even 
approached  that  required  to  develop  plasticity.  In  many  instances  it 
does  not  greatly  exceed  the  hygroscopic  water  that  the  clay  would  re- 
tain when  dried  in  open  rack  dryers.  In  fact  the  maximum  amount 
of  water  which  Grout  admits  could  be  so  molecularly  attracted,  agrees 
quite  closely  with  the  water  which  in  Table  XI  is  shown  to  be  in  excess 
of  that  required  to  fill  the  pores.  While  Grout's  statement  of  the  facts 
in  this  case  has  been  proved  incorrect,  further  investigation  may  find 
a  relation  between  the  molecularly  attracted  water  and  "excess  water/' 
As  yet,  however,  such  a  relation  cannot  be  established. 

That  a  clay  particle  does  possess  a  molecular  attraction  peculiar  to 
itself  is  not  denied.  That  this  molecular  attraction  alone  is  sufficient 
to  cause  a  plasticity  that  is  peculiar  and  belongs  to  no  other  substance 
must  be  discredited  until  evidence  is  brought  forward  that  will  bear 
an  analysis  such  as  is  given  in  Table  XIV. 

•  It  would  be  most  difficult  for  supporters  of  the  molecular  attraction 
theory  to  prove  that  the  kaolin  grains  in  primary  clays  do  not  possess 
every  physical  property  that  is  attributed  to  the  grains  of  the  clay  sub- 
stance in  the  secondary  clays,  save  that  of  plasticity.  Chemically  alike, 
and  differing  physically  only  in  this  one  respect,  yet  to  the  one,  accord- 
ing to  this  theory,  must  be  accredited  no,  or  very  little,  molecular  at- 
traction for  water,  and  to  the  other  a  strong  molecular  attraction. 

Grout1  may  be  quoted  as  follows: 

"The  attraction  of  two  grains  may  vary  with  the  nature  of  the  grains.  The 
greater  the  attraction  the  farther  they  can  be  separated  without  losing  coher- 
ence.      -.     Another  way  in  which  the  films  beeome  viscous  is  the 

result  of  molecular  attraction,  which  binds  a  film  over  the  surface  of  the 
grain  and  renders  it  viscous.  The  friction  between  this  film  and  the  solid 
grain  of  clay  is  said  to  be  infinite,  compared  with  water  outside  of  the  film. 
But  when  forced  to  move,  the  resistance  would  depend  on  the  strength  of 
the  attraction  of  clay  and  liquid. .     The  change  in  viscosity  or 

1  Jour.  Am. Chem.Soc.  Vol. XXVII,  No. 9, Sept. 1905, p. 1016. 


purdyJ  QUALITIES   OF   CLAYS   FOR    MAKING    PAVING   BRICK.  179 

in  thicknes  of  the  film,  seems  to  be  beyond  the  region  of  experiment.  The 
quantity  is  too  small  to  admit  the  determination  of  slight  changes,  but  such 
are  constantly  assumed  in  physical  problems.  W.  J.  A.  Bliss  speaks  of  clay 
particles  and  the  surrounding  adherent  liquid  as  follows:  'The  thickness 
of  this  shell  depends  on  the  intensity  of  the  attraction  between  the  solid 
and  the  liquid.'     J.  E.  Mills  says:      'Molecular  attraction  depends  primarily 

on   the   chemical   constitution    of  the   molecule. .'     Certain   rare 

organic    colloids    increase    the    plasticity    by    rendering    the    water    viscous. 

.     The  tendency   for   tensile   strength   to   vary  with   plasticity  is 

also  easily  explained  in  this  way.  Molecular  attraction  between  two  kaolin 
grains  may  be  high.  If  the  attraction  for  water  is  high,  some  water  will 
be  drawn  between  the  grains  and  rendered  viscous  by  the  attraction;  this 
makes  plasticity  high.  But  when  the  water  dries  out  from  such  a  mass, 
the  kaolin  grains  still  attract  each  other,  and  the  chances  are  for  greater 
strength  than  when  wet,  because  the  water  has  acted  as  a  lubricant,  allow- 
ing a  readjustment  of  grains  to  fill  the  space  left  as  the  water  moved  out. 
The  result  is  a  high  degree  of  consolidation." 

Mr.  Grout's  arguments  may  be  summed  up  as  follows: 

1.  Attraction  varies  with  the  nature  of  grain,  i.  e.,  their  chemical  con- 
stitution, or  in  other  words,  molecular  structure. 

2.  Films  become  viscous  as  a  result  of  molecular  attraction,  the  more 
strongly  attracted  film  being  the  more  viscous. 

3.  Organic  colloids  increase  plasticity  by  rendering  the  water  film  viscous. 

4.  The  tendency  for  tensile  strength  to  vary  with  plasticity  is  explained 
by  molecular  attraction  between  grains. 

5.  Change  in  viscosity  or  in  thickness  of  film  is  beyond  the  region  of  ex- 
periment. 

Granting  that  these  arguments  may  be  yalid  and  may  be  substan- 
tiated by  facts,  it  will  be  shown  later  that  they  may  be  considered  as 
establishing  the  existence  of  an  effect  rather  than  the  existence  of  a 
cause. 

Size  of  Grain  Theory  of  Plasticity — It  has  been  shown  earlier  in  this 
discussion  that  the  size  of  the  grains  as  determined  in  the  mechanical 
analysis  does  not  agree  with  the  normal  fineness  of  grain  in  the  clay  as 
it  issues  from  the  pug-mill;  there  are  bundles  of  grains  that  success- 
fully withstand  the  disintegrating  effect  of  water  in  the  pugging  pro- 
cess, but  which  are  to  a  large  extent  disintegrated  in  the  process  of 
mechanical  analysis.  It  is  obvious  therefore  that  conclusions  based 
wholly  on  the  results  obtained  in  the  mechanical  analysis  cannot  be 
considered  as  necessarily  agreeing  with  the  facts  observed  in  the.  actual 
behavior  of  the  clay  under  factory  conditions.  In  many  clays,  however, 
these  bundles  are  broken  down  to  such  an  extent  that  the  analytical 
results  indicate  quite  accurately  their  actual  working  properties. 

Because  in  the  mechanical  analysis  the  coarser  grains  have  been  re- 
ported as  sand  and  the  finer  particles  as  silt  and  clay,  not  a  few  have 
been  led  to  conclude  that  clay  particles,  or  at  least  particles  in  which 
clay  substances  constitute  a  large  proportion,  cannot  be  present  in  a 
clay  as  large  grains  after  thorough  disintegration  in  water.  Grout 
.has  shown,  however,  that  this  conception  is  entirely  erroneous.1  In 
Table  XVII  is  given  the  amount  of  clay  substance  that  he  obtained  first 
from  the  analytical  analysis,  second,  calculated  from  ultimate  analysis, 
and  third,  obtained  from  mechanical  analysis. 


W.Va.Geol.Surv.,  Vol. Ill, 1905,  p.  26. 


180 


PAVING    BRICK   AND    PAVING   BEICK   CLAYS. 


[BULL.   NO.    9 


Table  XVII. 

Showing  the  discrepancy  in  the  reported  "  clay  substance"  in  clay,  by  the 
three  methods  for  its  determination  now  in  vogue. 


Specimen  Number. 

Rational  Analysis 

Calculated  Kaolin 

Mechanical 
Analysis. 

4 

67.23 
36.80 
72.26 
70.48 
42.41 

52.30 
26  39 
41.65 
41.14 
31.50 

11  8 

17 

41 

36.85 
63  70 

62 

59.70 

76 

33.35 

Mr.  Grout  has  also  given1  results  of  the  chemical  analysis  of  a  com- 
plete mixture  of  the  several  grades  of  fineness  obtained  from  16  samples 
of  clay  as  follows : 


Table  XVIII. 


Constituents. 


.00  to  .001 


001  to  .005 

.005  to  .02 

.02  to  0.15 

54.54 

70.30 

81.16 

23.00 

16.04 

9.76 

5  91 

3.21 

2.13 

0.99 

0.63 

0.40 

1.02 

0  80 

0.39 

0.82 

0.72 

0.31 

0.29 

0.45 

0.56 

3  31 

2.14 

1.78 

1.10 

0.56 

0.35 

7.79 

4.33 

2.59 

1.12 

1.08 

0.78 

Si02 . . . . 
Al2Oa.. 
Fe203.. 
FeO.... 
MgO.... 
CaO  .... 
Na20... 
K20.  .. 
H20.... 
Ignition 
TiQ2.... 


44.08 
28.16 
7.94 
0.99 
1.36 
0.76 
0.00 
3.05 
2.80 
10.86 
0.84 


73.63 
13.01 
4.71 

0.18 
0.48 
0.47 
0.00 
0.93 
0.87 
4.40 
0.60 


In  this  he  has  proved  conclusively  that  the  "clay  substance"  is  pres- 
ent in  every  grade  of  fineness.  His  own  conclusions  from  these  analyses 
are,  however,  rather  startling.  He  says :  "The  silica  percentage  is 
higher  in  the  coarser  portions,  where  it  probably  is  present  in  the  form 
of  sand  or  quartz.  Alumina  is  higher  in  the  finer  material,  but  total 
fluxes  are  also  higher,  so  that  the  finest  particles  are  not  the  purest" 
kaolin." 

In  order  better  to  show  the  validity  of  his  conclusions  his  data  has 
been  calculated  into  molecular  equivalents  as  given  in  the  following 
table : 


1W.  Va.  Genl.  Surv.,  Vol.  Ill,  p.   61. 


PURDY]  QUALITIES   OF    CLAYS    FOR    MAKING    PAVING   BRICK.  181 

Tablk  XIX. 


Grades  of  Fineness. 

Si02 

Ala03 

Fe3Oa 

FeO 

MgO 

CaO 

Na20 

K20 

TiO, 

0  00  to  0  001 

2.66 
4.03 
7.45 
14.14 
9.62 

1.00 
1.00 
1.00 
1.00 
1.00 

0.18 
0.16 
0.13 
0.14 
0.02 

0.05 
0.06 
0.06 
0  59 
0.0C2 

0.12 
0.11 
0.13 
1.02 
0.01 

0.05 
0.06 
0.08 
0.58 
0.007 

0.02 
0.05 
0.94 

0.12 
0.16 
0.14 
0  19 
0.008 

0  04 

0  001  to  0  005 

0  06 

0  005  to  0  02 

0  09 

0  02  to  0.15     

1  02 

0  006 

A  review  of  Grout's  mechanical  analysis  of  the  West  Virginia  clays 
discloses  the  fact  that  he  made  26  determinations : 

6  plastic    fire    clays,    pp.    160,    162,  163,  233  and  251, 
1  flint  fire  clay,  p.  218, 

7  shales,  pp.  249,  251,  242  and  262, 

10    river    clays,    pp.    263,  -265,    270,   272,  274,  and  276. 
1  glacial  clay,  p.  265, 
1  residual  surface  clay,  p.  200. 

It  is  assumed,  therefore,  that  the  samples,  the  analyses  of  which  are 
given  in  Table  XVI,  are  composites  of  the  several  grades  of  grains  from 
the  above  clays.  Being  in  most  cases  very  impure  clays,  it  is  con- 
sidered that  although  a  study  of  the  possible  mineral  make-up  of  each 
grade  is  at  the  best  largely  based  on  hypothetical  assumptions,  such  a 
study  would  aid  in  our  attempt  to  understand  the  constitutional  make- 
up of  our  clays. 

On  the  assumption  that  all  the  alkali  is  present  as  a  EO  in  orthoclase 
feldspar,  the  molecular  ratio  and  ratio  by  weight  of  kaolin,  feldspar 
and  quartz  present  in  each  grade  would  be  as  follows: 

Table  XX. 

Showing  possible  mineral  constitution   of  the   several  grades   of    grains    in 

impure  clays. 


Molecular  Rat 

io. 

Weight  Ratio. 

Quartz. 

Grade. 

Kaolin. 

Feldspar. 

Quartz. 

Kaolin. 

Feldspar. 

0  00  -0.001 

0.88 
.82 
.81 

0.12 
0.18 
0.19 
1.00 
0.008 

.18 
1.25 

4.69 
8.14 
3.62 

10 
10 
10 

2.9 

4.7 

5.1 

10.0 

0.18 

0.08 

0  001-0.005 

3.5 

0  005-0.02 

13.5 

0  02  -0.15 

8 

0  15  up     

0  992 

10 

8  5 

This  data  checks  the  fact  developed  in  Table  XV,  i.  e.,  that  clay  sub- 
stance is  to  be  found  in  all  of  the  grades  of  fineness,  in  the  coarsest  as 
well  as  the  finest.     It  also  shows  that  more  than  50  per  cent  of  the 


182  PAVING   BRICK   AND    PAVING   BRICK   CLAYS.  [bull.  no.  9 

coarsest  group,  or  as  it  is  customarily  called,  "coarse  sand,"  may  be 
kaolin,  or  is  at  least  kaolinitic  in  composition. 

As  a  further  analysis  of  the  probable  mineral  make-up  of  clays, 
Grout's  data  will  be  discussed  by  groups.  In  this  only  the  most  com- 
mon and  abundant  minerals  known  to  occur  in  clays  are  considered. 

Coarsest  grade  (0.15  mm.)  :  This  grade  of  grain,  even  if  all  the 
alkali  is  considered  as  being  present  as  a  constituent  part  of  feldspar 
grains,  would  be  assumed  to  be  composed  almost  entirely  of  non-dis- 
integrated kaolin  and  quartz  grains.  Only  in  one  case,  however,  does 
Mr.  Grout1  speak  of  the  physical  character  of  the  grains  of  this  grade. 
In  this  particular  case  the  clay  examined  is  a  shale.  "The  12.9  per 
cent  (referring  to  coarse  sand  grade)  on  3  mm.  screen  was  mostly  flat 
scales  of  shale,  about  5  mm.  in  size,  of  red  and  greenish  color."  The 
total  absence  of  similar  description  of  this  grade  in  the  other  25  samples 
justifies  the  conclusion  that  the  grains  of  this  grade  were  flat  or  scale 
like  only  in  this  one  sample.  If  this  conclusion  is  true,  then  it  is  fair 
to  assume  that  either  the  kaolin  scales  are  present  in  undissolvable 
bundles,  or  these  grains  are  not  composed  of  kaolin  but  some  other 
aluminum  compound  like  gibbsite,  etc. 

On  the  other  hand,  it  is  hardly  possible  that  grains  of  feldspar  of 
this  size  could  remain  unaltered  in  these  old  river  clays  that  have  been 
elutriated,  mixed  and  moved  by  fresh  waters  possibly  for  ages.  There 
is  justification  for  the  assumption,  therefore,  that  these  coarse  grains 
are  bundles  of  kaolinitic  grains  cemented  together  so  tightly  by  some 
salt  that  they  resist  disintegration  by  water.  If  the  alkalies  had  been 
present  as  constituent  parts  of  feldspar  grains  of  this  size,  the  feldspar 
crystals  could  have  been  easily  recognized  under  the  microscope  as 
cubical  grains  and  not  flat  scales. 

H.  B.  Fox,  in  the  Ceramic  laboratories  of  the  University  of  Illinois, 
separated  the  grains  of  a  shale  and  a  glacial  clay  into  the  several 
grades  of  fineness,  and  found  that  all  the  grades  possessed  a  plasticity 
that  varied  directly  with  the  fineness  of  grain,  and  that  the  coarse 
grains  which  could  not  be  disintegrated  by  20  hours  of  constant  shaking 
in  water,  when  broken  down  in  a  mortar,  developed  plasticity  that  in- 
creased as  the  size  of  the  grains  decreased,  until  when  the  coarse  grains 
had  been  reduced  to  an  impalpable  powder  they  developed  a  plasticity 
nearly  equal  to  that  exhibited  in  the  finest  grains  that  had  been  separ- 
ated from  the  original  sample,  showing,  it  is  believed,  that  the  coarser 
grains  were  comprised  of  materials  similar  in  every  respect  to  those  in 
the  fine  grains,  but  cemented  in  such  a  way  that  they  withstood  success- 
fully the  disintegration  treatment. 

(0.02  to  0.15)  grade:  It  is  highly  improbable  that  this  grade  con- 
tained no  kaolin  or  clay  substance,  but  such  would  have  to  be  the  case 
if  all  the  alkali  was  present  as  a  constituent  part  of  the  orthoclase  feld- 
spar grains.    The  alkalies  cannot  be  present  in  this  case  as  easily  soluble 

1W.  Va.  Genl.  Surv.,  Vol.  Ill,  p.   249. 


PURDY] 


QUALITIES   OF   CLAYS    FOR    MAKING    PAVING    BRICK. 


183 


salts,  for  the  alkaline  salts  would  have  been  dissolved,  carried  in  solu- 
tion, and  would  affect  only  the  finest  grades.  If  the  feldspar  was  oligo- 
clase  and  not  orthoclase,  then  the  0.5  equivalents  of  the  alumina  could 
be  considered  as  a  constituent  of  kaolin  grains. 

Although  there  is  no  statement  made  as  to  the  presence  of  mica  in 
the  clays  from  which  these  grades  of  grains  were  obtained,  Mr.  Grim- 
sley1  states  that  it  is  a  very  common  constitutent  of  the  West  Virginia 
clays.  Stull2  gives  as  the  chemical  formula  of  common  muscovite  mica 
the  following: 

0.1243  CaO 1 

0.1103  MgO 11.000  A1203 I  6.399  Si02-0  <>74  H2Q 

0.3280  K20 fO.1857  Fe„03  f  Comb.  Wt.  582.167 

0.0929  Na20 J 

On  the  assumption  that  the  alkali  in  this  grade  is  derived  wholly  from 
muscovite  mica  of  the  composition  given  by  Stull,  the  mineral  constitu- 
tents  of  this  grade  of  grain  might  be  proportioned  as  shown  by  the 
following  calculations : 


Si0a 

A1203 

Fe203 

FeO 

MgO 

CaO 

Na20 

K20 

Ti02 

14.14 

1.00 

0.14 

0.59 

1.02 

0.58 

0  94 

0.19 

1.02 

.57  Eqv.  Mica , 

3.65 

0.57 

0.11 

0.06 

0.07 

0.05 

0.19 

10.49 

0.43 

0.03 

0.59 

0.96 

0.51 

0.89 

1.02 

.43  Eqv.  Kaolin 

.86 

0.43 

.63 

0.89 

0.57  Eqv.  Mica  x 
0.43  Eqv.  Kaolin  x 
0.63  Eqv.  Silica       x 


582.167  =  331.835  or  by  proportion  30.0 
258  =  110.940  or  by  proportion  10.0 
60    =      37.800    or  by  proportion      3.4 


In  this  case,  the  formula  most  favorable  to  the  supposition  that  all 
ilie  K2O  is  present  in  the  form  of  mica  has  been  taken.  If  the  theoret- 
ical formula  K2O,  3  AI2O3,  6  Si  (X>,  2  ILO  had  been  taken,  there  would 
have  been  either  considerable  K2O  to  account  for  in  some  other  way,  or 
return  to  the  original  hypothesis  that  this  group  contained  no  kaolin. 
Either  supposition  leaves  considerable  alkali  unaccounted  for,  which 
as  has  been  pointed  out,  could  not  possibly  be  present  in  an  early  soluble 
form. 

The  supposition  therefore  that  this  grade  is  composed  in  part  of 
kaolinitic  grains  cemented  together  by  some  alkaline  salts,  finds  sup- 
port in  any  plausible  assumption  that  may  be  made. 

(0.005—0.02  and  (0.001—0.005)  groups:  If  the  kaolin  grains  in 
these  groups  were  in  their  natural  condition,  i.  e.,  flat  plate-like  crystals, 
they  should,  theoretically,  be  visible  through  the  microscope.  This  evi- 
dently was  not  the  case.  Beyer  and  Williams1  say:  "While  it  is  next 
to  impossibleto  make  out  much  concerning  the  crystalline  character  of 
the  minerals,  it  is  also  difficult,  because  of  their  minute  size  in  most 
secondary   clays,    to^  say   anything   regarding   their    shape." — In    other 


1W.  Va.  Geol.  Surv.,  Vol.  Ill,  p.   12. 
2  A.  C.  S.  Trans.  Vol.  IV,  p.  258. 
Ha.  Geol.   Surv.,  Vol.  XIV,  p.   94. 


184  PAVING   BRICK   AND    PAVING   BRICK   CLAYS.  [bull.  no.  9 

Words,  the  shape  of  the  grains  is  irregular  and  non-conformable  one 
with  another.  If  in  these  grades  there  is  as  much  kaolin  as  is  shown  in 
■Table  XVIII,  its  grains  must  be,  to  a  very  great  extent,  in  bundles.  If 
feldspar  or  mica  is  present  in  such  amount  and  size  of  grain,  as  the  cal- 
culated data  suggest,  their  grains  ought  to  be  detectable  with  the  aid 
of  the  microscope.  Such,  however,  is  not  the  case.  The  supposition, 
therefore,  that  all  the  akalies  of  these  two  grades  are  there  as  constitu- 
ent parts  of  feldspar  and  mica  is  certainly  untenable. 

(0.000-0.0001)  grade:  The  molecular  composition  of  this  group  is 
certainly  very  instructive.  That  in  such  heterogeneous  mixtures  as 
shales  and  river  clays  the  finest  particles  are  found  to  be  composed  in 
the  main  of  kaolinitic  grains  is  certainly  astonishing.  If  the  bases 
present,  as  shown  in  Table  XIX,  page  181,  are  considered  as  being 
present  as  soluble  salts  that  were  either  originally  present  in  the  clays 
or  in  part  introduced  during  the  process  of  analysis,  (a  most  plausible 
assumption)  then  there  would  remain  but  one  conclusion,  that  is,  that 
the  finest  insoluble  grains  are  almost  entirely  kaolinitic  in  composition. 

Taking  data  given  by  Grout,  it  was  calculated  that  if  all  the  soluble 
salts  originally  in  the  clays  wTere  in  the  finest  group,  they  would  amount 
to  2.7  per  cent  of  the  weight  of  that  group.  The  2.7  per  cent,  together 
with  the  soluble  salt  introduced  during  the  process  of  analysis  from 
glassware,  water,  atmospheric  dust,  etc.,  would  account  for  nearly  all 
of  the  alkali  in  the  finest  grade.  It  is  not  mere  assumption  therefore, 
that  the  finest  particles  in  clay,  contrary  to  Grout's  statement,  are  the 
purest  kaolin  grains. 

In  the  course  of  the  research  on  paving  brick  clays  by  the  survey  there 
was  much  speculation  as  to  the  number  of  these  submicroscopic  kaolin 
grains  in  the  various'  shales.  This  was  readily  ascertained  as  follows : 
By  dividing  the  percentage  amount  of  the  group  (0.001  to  0)  by  100, 
and  considering  that  as  being  a  part  of  1  milligram  of  the  sample,  (for 
the  size  of  the  particles  is  in  millimeters)  then  dividing  this  amount  by 
the  specific  gravity  of  the  clays,  a  figure  is  obtained  that  represents  the 
sum  or  total  volume  in  cubic  millimeters  of  the  particles  comprising 
the  group.  Considering  0.0005  as  the  mean  diameter  of  the  particles, 
6 

by  the  formula -the  volume  of  each  particle  is  found  to  be  654xl0"13 

PiD3 
cubic  millimeters.  Then  for  each  day,  by  dividing  the  total  volume 
of  the  particles,  by  the  volume  of  one  particle,  the  number  of  grains 
per  milligram  of  the  sample  will  be  obtained.  By  multiplying  the  num- 
ber of  grains  in  one  milligram  by  1,000  there  would  be  obtained  the 
number  of  grains  in  1  gram;  or  by  multiplying  by  352,740  there  would 
be  obtained  the  number  of  grains  of  this  size  in  1  oz.  of  the  whole 
sample.    In  this  way  Table  XXI  was  calculated. 

l  This  mean  diameter  is  twice  as  large  as  that  given  by  Whitney  for  the  finest 
group;  U.  S.  Dept.  of  Agr.  Weather  Bureau,  Bull.,  No.  4,  p.  3  5. 


PURDY]  QUALITIES   OF    CLAYS    FOR    MAKING    PAVING    BRICK. 


185 


Table  XXI. 
Number  of  grains  of  group  (0.001  to  0)  in- 


Sample  No. 

1  gram  of  the  clay. 

1  oz.  of  the  clay. 

K  1 

560     trillions. 

829.0  trillions. 

794.0  trillions. 
1,588.7  trillions. 
1,940.0  trillions. 

440.0  trillions. 

197, 534  trillions. 

K2 

292,421  trillions. 

K3 

280,075  trillion4. 

H23 

560,398  trillions. 

H21 

684,315  trillions. 

K6 

166,205  trillions. 

These  figures,  although  beyond  the  limits  of  perception  of  the  human 
mind,  are  not  larger  than  the  figures  representing  the  countless  germs 
that  bacteriologists  claim  can  exist  in  a  single  drop  of  a  fluid.  Startling 
as  this  data  appears  to  be,  it  cannot  be  other  than  true  if  the  analytical 
results  of  the  mechanical  separation  are  correct. 

If  these  minute  particles  were  not  kaolin  grains,  would  they  add  to 
the  real  plasticity  of  the  clay?  Potter's  flint  (dry  ground)  is  finer 
grained  than  most  clays,  and  particularly  more  so  than  the  shales,  yet 
it  does  not  exhibit  the  faintest  sign  of  plasticity.  Orton1  found  that 
glass  particles  which  were  so  fine  that  they  remained  in  suspension  for 
hours  without  settling,  when  collected  exhibited  no  plasticity.  Wheeler2 
found  that  while  quartz  crystals  ground  to  200  mesh,  seemed  to  be  ap- 
preciably plastic,  on  drying  the  coherence  was  so  slight  that  it  required 
the  gentlest  handling  to  prevent  the  molded  sample  from  falling  to 
pieces.  Fine  quartz  dust  and  impalpable  geyserite  or  finely  precipi- 
tated opal,  dried  to  a  very  tender  mass.  The  same  was  true  of  tripoli. 
Wheeler3  found  that  some  plasticity  could  be  developed  in  powdered 
slate,  prophylite,  talc,  gypsum,  halloysite,  etc.,  but  that  the  plasticity 
developed  was  only  apparent  plasticity,  except  perhaps  in  the  case  of 
slate.  The  powdered  gypsum  when  molded  and  dried  formed  a  rela- 
tively hard  mass,  but  this  hardness  would  be  expected  on  account  of  the 
solubility  of  gypsum  in  water.  The  plasticity  of  the  slate,  which  is  a 
dehydrated  shale  has  caused  considerable  surprise,  and  has  strengthened 
the  fineness  of  grain  theory  of  plasticity.  That  powdered  slate  should 
develop  plasticity  need  not  be  so  great  a  source  of  wonder,  for  in  the 
course  of  the  Survey  work  a  shale,  after  having  been  held  at  heat  rang- 
ing from  500°  to  800°  C.  for  17  hours,  slaked  down  in  water  to  a 
red  plastic  mass  in  the  same  manner  as  the  unburned  shale  at  the  bank. 
True,  the  plasticity  of  this  partially  burned  shale  was  not  equal  to  the 
plasticity  shown  by  the  clay  before  dehydration,  but  its  plasticity  was 
considerably  more  than  that  of  some  of  the  harder  shales  before  being 
burned.  Fineness  of  grain  in  itself  then  does  not  seem  to  be  the  cause 
of  plasticity.  It  may  said,  however,  to  be  a  required  condition  in  the 
operation  of  the  real  cause. 

1  Brick,  Vol.  XIV,  No.  4,  p.  216. 

2  Mo.  Geol.   Surv.,  Vol.  XI,  p.   102. 

3  Loc.  cit,  p.  106. 


186  PAVING   BRICK   AND   PAVING   BRICK   CLAYS.  [bull.  no.  9 

In  seeming  contradiction  to  this  statement  regarding  the  fineness  of 
grain  as  a  sense  for  plasticity,  is  the  fact  that  finer  grinding  of  given 
clay  increases  its  plasticity;  but  quoting  Wheeler1:  "While  it  is  true 
that  fine  clays  are  usually  very  plastic  and  coarse  clays  much  less  so, 
there  are  very  many  exceptions."  And  again,  Grout2  says  that  while 
the  majority  of  clays  improve  on  fine  grinding,  some  are  unchanged. 
Wheeler3  reports  the  physical  structure  of  a  few  clays  as  follows : 
Moberly  shale  (400  diam.) : 

Mainly  clusters  of  thick  plates  with  minor  portions  split  off;  moderately 
plastic;   suggests  fine  grinding  to.  develop  plasticity. 
Aldrich  shale   (325  diam.): 

One-third    dolomite   crystals;    bulk    in    coarse    thick   crystals   or   plates; 
rest  in  fine  state  of  division;  moderately  plastic. 
Unweathered  Leasburg  flint  fire  clay  (950  diam.): 

Almost  all  fine  particles;  no  plates  or  scales;  devoid  of  plasticity. 
Weathered  Leasburg  flint  fire  clay  (950  diam.) : 

Numerous  coarse  plates  present  and  occasionally,  apparently  a  few  thin 
plates.     Came  from   same  bank  the   same   day  a   few  feet  from  the 
unweathered  sample. 
Hartwell  loess  clay  (400  diam.): 

Large  angular  fragments  which  were  undoubtedly  sand,  and  apparently 
some  clusters  of  plate  crystals,  with  only  a  minor  portion  of  small 
plates;  very  plastic. 
There  is  sufficient  evidence  in  the  above  citations  to  show  that  any 
theory  so  far  discussed  other  than  that  of  molecular  attraction,  is  in- 
sufficient to  account  for  the  presence  or  absence  of  plasticity. 

Plate  Structure  Theory  of  Plasticity — Grout1  has  recorded  the  facft 
that  in  the  case  of  the  Thornton  Brick  Company's  plastic  clay  the 
amount  by  weight  of  the  particles  below  0.005  mm.  in  diameter  rose 
from  7.7  per  cent  to  17.8  per  cent  by  weight  in  one  wetting  and  drying. 
Fox,  in  our  laboratories,  found  that  the  plates,  although  not  disintegrat- 
ed by  twenty-four  hours  of  shaking  in  water,  would  break  down  by 
mechanical  crushing  or  by  disintegration  in  acids  and  caustic  alkali, 
and  that  when  so  broken  down  the  mass  became  considerably  more 
plastic.  Wheeler1  not  only  advises  fine  grinding  in  the  case  of  the 
Moberly  shales,  but  relates  a  most  remarkable  instance  of  a  clay  in 
which  the  grains  on  weathering  formed  themselves  into  clusters  re- 
sembling plates.  It  seems  highly  probable,  therefore,  that  these  plates 
or  coarse  grains  are  bunches  or  bundles  of  minute  grains  cemented  to- 
gether by  salts  that  are  to  a  greater  or  less  extent  soluble  in  water,  and 
that,  depending  upon  the  solubility  of  the  cementing  salt  in  a  particular 
case,  or  the  peculiar  compactness  of  the  grains  in  another,  it  requires 
a  greater  or  less  amount  of  time  to  cause  a  breaking  down  of  these 
bundles.  It  can  be  readily  conceived  that  the  adsorptive  power  of  the 
particles  when  combined  with  their  axes  in  a  certain  general  direc- 
tion, for  instance,  has  greater  power  in  holding  certain  of  these  cement- 
ing salts  than  the  solvent  action  exerted  by  the  water  can  overcome. 
The  solvent  power  of  water,  in  other  words,  is  not  sufficient  to  overcome 
the  adsorptive  power  of  the  kaolinitic  grains. 

l  Loc.  cit.,   p.    109. 

2W.  Va.  Geol.  Surv.,  Vol.  Ill,  p.  46. 

3  Loc.  cit.,  pp.  104  to  109. 

4W.  Va.  Geol.  Surv.,  Vol.  Ill,  p.  46. 

5  Loc.  cit.,  p.  105. 


purdy]  QUALITIES  OF  CLAYS  FOR  MAKING  PAVING  BRICK.  187 

These  coarse  grains  add  to  the  plasticity  of  the  clay  as  a  whole  in  a 
ratio  to  the  surface  exposed.  Every  exposed  kaolin  particle  is  as  effec- 
tive in  enhancing  plasticity  as  the  very  small  independent  particles.  The 
extent  to  which  the  larger  grains  would  affect  plasticity  would,  there- 
fore, be  in  proportion  to  the  exposed  surface  of  the  particles  of  which 
the  bundle  or  cluster  is  composed. 

Further,  it  is  fair  to  challenge  the  plate  theorist  to  demonstrate  that 
these  small  grains  when  cemented  together  in  a  bundle  or  cluster  have 
not  a  tendency  to  line  up  one  with  another  so  that  their  longest  axes 
will  lie  in  the  same  relative  plane,  just  as  they  are  in  the  natural  kaolin 
crystals,  i.  e.,  in  plate  forms.  The  plate  theorist  must  admit  that  when 
these  bundles  are  thus  formed  they  are  well-nigh  indistinguishable  from 
mica  crystals,  and  that  the  very  large  majority  of  so-called  plates  or 
scales  of  kaolin  in  a  clay  are  most  likely  to  be  mica.  It  is  certainly 
strange  that  on  one  page  of  a  report  there  will  be  a  statement  to  the 
effect  that  "the  clays  of  this  state  are  quite  micaeious,"  and  another 
page  will  report  the  scales  that  appear  on  the  stage  of  the  micro- 
scope as  "kaolin  scales  or  plates." 

1  If  the .  idea  that  has  been  put  forward  in  the  foregoing  is  correct, 
then  we  must  agree  with  Dr.  Ladd1  when  he  says:  "The  question  of 
fineness  of  grain  and  shape  of  the  particle  becomes,  then,  largely  but 
modifying  factors,  affecting  degree,  and  being,  within  large  limits  at 
least,  modifiers,  rather  than  determinants  of  plasticity." 
1  It  is  quite  evident  that  the  peculiar  physical  make-up  of  a  kaolin 
grain,  so  far  as  the  eye  by  the  aid  of  the  microscope  can  discern,  is  not 
fundamentally  responsible  for  their  individuality,  as  expressed  in  their 
power  to  develop  plasticity.  If  the  structure  of  the  grains  which  en- 
ables a  mass  of  them  to  develop  plasticity  is  not  detectable  by  the  micro- 
scope, direct  observation  and  measurement  are  obviously  inadequate  in 
finding  the  true  cause. 

Pectoidal  Theory  of  Plasticity — Turning  to  indirect  or  circumstantial 
evidence,  there  are  many  facts  observed  by  a  good  many  careful  scientists 
that  seem  to  point  to  one  thing  that  is  more  characteristic  of  kaolin 
grains  than  of  any  other  of  the  inorganic  substances  or  minerals  of 
which  a  clay  is  composed,  i.  e.,  adsorptive  power.  Some  investigators 
have  even  gone  so  far  as  to  attribute  the  plasticity  of  kaolin  grains  to  an 
adsorptive  power  or  actual  taking  into  the  grains  themselves  of  foreign 
salts  from  solution.  They  advance  the  theory  that  these  minute  grains 
have  a  micellian  structure.  To  such  substance  they  apply  the  name 
"Pectoid,"  and  to  the  theory  the  name,  "Pectoid  theory."  To  many,  the 
absorptive  and  adsorptive  properties  of  a  clay  are  one  and  the  same 
thing,  and  so  far  as  can  be  judged,  the  most  radical  believe  in  either 
the  adsorptive  or  the  pectoidal  theory,  and  oscillate  from  one  to  the 
other  in  a  manner  that  induces  skepticism.  The  fact  remains,  how- 
ever, that  both  use  the  same  arguments,  the  only  difference  being  in  the 
conception.     It. is  safe  to  warrant,  that  when  the  pectoid  theorist  real- 

lGeol.  Surv.,  of  Ga.,  Bull.  6-A,  p.  32. 


188  PAVING    BRICK   AND    PAVING    BRICK   CLAYS.  [bull.  no.  9 

izes  than  in  one  gram  of  clay,  the  disintegration  of  which  has  been 
effected  only  by  shaking  in  distilled  water,  there  can  exist  from  400 
to  1500  trillion  free  and  independent  sub-microscopic  particles,  to  say 
nothing  about  the  larger  particles,  they  will  find  interstices  between 
these  grains  sufficient  to  satisfy  even  the  most  exaggerated  conception  of 
a  micellian  structure. 

1  Dr.  Cushman1  in  a  brief  review  of  the  observations  that  point  toward 
a  colloidal  substance  as  being  the  prime  cause  of  plasticity,  has  given 
the  following  citations :  "Daubree  found  that  wet  ground  feldspar  as- 
sumed a  plastic  condition,  whereas  dry  ground  feldspar  did  not."  Oat- 
wald,  the  eminent  German  physical  chemist,  Arons,  Bischol,  Seger, 
Eokland,  and  A7an  der  Bellen,  accepted  and  advanced  in  substance  the 
colloid  theory.  T.  Way2  stated  that  while  particles  of  sand  and  chalk 
absorbed  water,  owing  to  surface  attraction  and  capillarity,  clays  and 
soils  with  a  clay  base  behaved  in  a  quite  extraordinary  manner.  The 
more  clayey  the  soil  the  more  water  it  seemed  capable  of  absorbing. 
'But  this  was  not  all;  besides  water  this  clay  substance  exhibited  5 
'greater  facility  for  absorbing  the  bases  contained  in  certain  salts  which 
Were  dissolved  in  the  water." 

1  E.  Bourry2  says  that  if  clay  is  mixed  with  a  solution  of  calcium  car- 
bonate, the  clay  will  retain  some  of  the  carbonate.  "Kaolins  do  not 
retain  more  than  2  per  cent  of  carbonate  of  lime  in  solution,  while 
plastic  clays  can  absorb  from  10  to  20. per  cent  of  it." 
i  It  is  common  knowledge  among  chemists  that  clay  can  extract  solu- 
ble salts  from  solution  and  retain  them  very  persistently  against  all 
attacks  by  dissolving  mediums.  Mr.  Ackison3  found  that  catechu  and 
extract  of  sumac  leaves,  spruce  bark,  tea  leaves,  oak  bark  or  straw 
would  be  absorbed  by  clays  from  solutions. 

•  Further,  Eies4  advanced  the  theory  that  the  action  of  hydro-carbons 
in  solution  was  to  deflocculate  the  particles.  This  he  claims  was  proved 
by  the  fact  that  in  the  untreated  clays  the  grains  were  bunched  to- 
gether while  in  the  treated  clays  the  particles  were  separated. 
1  In  the  foregoing  citations  there  is  evidence  sufficient  to  formulate  a 
Conception  of  what  changes  have  taken  place  in  a  clay  from  the  time 
it  was  first  formed  in  situ  by  decomposition  of  the  parent  rock  and 
left  practically  devoid  of  plasticity,  until  it  was  deposited  elsewhere  as 
a  plastic  clay.  Organic  matter  would  have  deflocculated  the  particles, 
and  the  soluble  salts,  which  are  very  naturally  attracted  to  the  kaolin 
grains,  would  soften  when  wetted,  but  the  water  could  not  extract  them 
owing  to  the  greater  force  exerted  by  the  kaolin  particles.  Defloccula- 
tion  by  organic  matter,  recementation  by  salts  of  various  kinds,  may 
have  formed  a  cycle  of  events  'that  in  the  end  would  cause  a  condition 
Of  affairs  that  makes  possible  the  property  described  as  plasticity. 

Molecular  attraction  for  foreign  substances  which  is  peculiar  to  kaolin 
particles,  and  not  to  a  very  large  degree  to  other  common  constituents 
of  clay,  may  and  does  have  its  influence  on  plasticity  affected  by  flne- 

lVol.  VI,  a.  c.  s.,  p.  66. 

2  Royal  Ag.  Soc,  Jour.  XI,  1850,  cited  by  Cushman. 

3  Emile   Bourry  ,  Treatise  on  Ceramic  Industries,   p.    54. 
4Amer.  Cer.  Soc.  Trans.,  Vol.  VI,  p.  33/ 

5  A.   C.   S.   Trans.,  Vol.  VI,   p.   43. 


purdy]  QUALITIES   OF   CLAYS    FOR    MAKING    PAVING    BRICK.  189 

ness  of  grain.  Plate  structure,  a  natural  form  in  which  kaolin  grains 
arrange  themselves,  is  a  possibility  under  the  right  conditions,  but  there' 
is  also  a  possibility  that  organic  matter  and  adsorbed  salts  may  operate 
in  the  destruction  and  formation  of  the  plate  grains.  A  clay  that  is  of 
secondary  origin,  like  our  common  clays,  could  not  have  passed  through 
the  many  geological  changes  with  which  they  are  credited  without  being 
more  or  less  deflocculated  and  saturated  with  these  foreign  substances. 
Micellian  structure  is  not  a  necessary  condition.  Minuteness  of  grain 
and  consequently  large  surface  or  adsorbing  area  is  sufficient. 

Adsorption  theory  of  plasticity — Existing  data,  accumulated  for 
years  by  scientists,  all  point  to  the  fact — which  is  almost  beyond  the 
theoretical  state,  lying  wholly  within  the  realm  of  experimentation — 
that  the  plasticity,  tensile  strength  and  general  working  properties  of 
the  clay  can  be  traced  back  to  the  adsorptive  property  of  kaolin.  Fur- 
ther, all  the  facts  that  have  been  cited  in  support  of  any  and  all  of  the 
theories  are  identifiable  as  conditions  that  allow  of  the  fullest  exhibition 
of  the  plasticity  that  seems  to  follow  as  a  direct  consequence  of  the 
adsorption  of  soluble  organic  and  inorganic  substances  by  the  kaolin 
grains. 

DEVELOPMENT    OE    PLASTICITY    IN    THE    PRESENCE    OF    WATER. 

Whatever  may  be  the  fundamental  cause  of  this  phenomenon  we  call 
plasticity,  it  is  certain  that  it  is  manifested  only  when  water  is  present. 
It  has  been  shown  that  mere  molecular  attraction  between  the  clay 
grains  and  the  water  molecules. is  not  sufficient  to  account  for  plasticity. 
There  must,  therefore,  be  factors  other  than  molecular  attraction  which 
becomes  operative  in  developing  this  property,  which,  when  water  is 
not  present,  may  be  said  to  be  latent.  Since  it  is  the  presence  of  water 
that  makes  the  development  or  expression  of  plasticity  possible,  it  is 
important  that  we  consider  some  of  the  fundamental  and  well-known 
hydrostatic  forces. 

There  are  at  least  four  forces  operating  on  the  water  in  a  wet,  un- 
burned  brick :  First,  gravity,  or  the  weight  of  the  water  itself ;  second, 
surface  tension,  which  is  due  to  attraction  (cohesive)  between  the 
molecules  of  water  themselves;  third,  molecular  attraction  (adhesive) 
between  the  water  molecules  and  the  mineral  particles  in  the  clay;  and 
fourth,  surface  pressure,  which  is  the  opposite  of  surface  tension. 

Gravity — Surface  tension,  or  the  contracting  power  of  any  exposed 
water  surface,  may  act  with  gravity  or  against  gravity,  depending  upon 
circumstances.  Molecular  attraction  between  the  mineral  and  water 
molecules  always  acts  in  opposition  to  gravity.  Since,  as  can  be  shown, 
the  conditions  of  capillarity  in  a  mass  of  clay  compressed  into  the  form 
of  a  brick  is  such  as  to  make  surface  tension  the  very  much  greater 
force,  and  operating  in  opposition  to  that  of  gravity,  gravity  will  not 
be  considered  as  one  of  the  component  forces  in  our  problem.  If  we 
were  dealing  with  "slips"  or  even  soft  mud  fixtures,  the  force  of  gravity 
would  have  to  be  considered. 

Molecular  Attraction — Milton  Whitney1  says:  "The  potential  of  a 
single  water  particle  is  the  work  which  would  be  required  to  pull  it 

1U.  S.  Dept.  of  Agr.  Weather  Bureau,  Bull.  4,  p.  19. 


190 


PAVING   BRICK   AND    PAVING   BRICK   CLAYS. 


[BULL.   NO.   9 


away  from  the  surrounding  water  particles  and  remove  it  beyond  their 
sphere  of  attraction.  It  is  the  total  attraction  between  a  single  particle 
and  all  other  particles  which  surround  it."  It  is  called  by  some  "mole- 
cular attraction." 

Surface  Tension — Because  it  has  particles  adjoining  it  only  on  one 
side,  i.  e.,  molecular  attraction  is  affecting  it  only  from  one  side,  the 
potentiality  of  a  water  particle  on  the  surface  is,  according  to  Whitney's 
definition,  only  one-half  that  of  a  particle  in  the  center  of  a  drop.  That 
things  tend  to  move  from  points  of  low  to  points  of  high  potential  is 
a  well-known  law  of  physics.  The  particles  on  the  surface,  will,  there- 
fore, strive  to  get  to  the  interior  of  the  drop.  The  results  will  be  sur- 
face tension. 

Looking  at  this  proposition  from  the  mechanical  point  of  view,  the 
force  of  molecular  attraction  operating  on  the  surface  particles,  is  effec- 
tive along  lines  that  extend  from  the  center  of  each  particle,  to  the 
center  of  the  surrounding  particles.  Since  the  particle  on  the  surface 
of  a  drop  of  water  is  under  the  influence  of  other  particles  only  from 
one  side,  the  several  lines  of  force  would  extend  radically  from  its  center 
to  the  center  of  adjacent  particles,  having  as  a  resultant  a  line  of  force 
extending  from  the  center  of  the  surface  particle  to  the  center  of  the 
mass. 

Surface  Pressure — Suppose  that  instead  of  a  drop  we  have  the  same 
mass  of  water  surrounding  a  solid  particle  as  a  film,  say,  0.0005  m  m. 
thick.  We  should  have  in  this  system  two  combating  forces,  first,  mole- 
cular attraction  of  water  molecules  for  each  other,  causing  a  pull  on  all 
water  particles  toward  the  center  of  the  film,  creating  a  tension  on  the 
outside  surface  as  well  as  on  the  surface  contiguous  to  the  solid  par- 
ticles; second,  attraction  between  the  molecules  of  the  solid  particles 
and  those  of  the  liquid,  tending  to  create  a  tension  only  on  the  outer 
surface  of  the  glm. 

Consider  the  water  between 
four  solid  particles  as  shown  in 
the  following  figure  as  having  a 
potentiality  less  than  that  of  the 
solid  particles. 

All  water  particles  will  press 
outward  the  solid  particles  along 
the  resultant  lines  of  force  as 
shown  in  Fig.  16.  In  this  case 
instead  of  tension  we  would  have 
a  pressure.  This  pressure  is 
known  as  surface  pressure. 

If,  on  the  other  hand,  the 
water  had  a  potentiality  that  was 
greater  than  that  of  the  solid  par- 
ticles, the  resultant  forces  of  at- 

Diagram  showing  operation  of  forces       ,         ••  in  i^  4.^„.„„;i  -n.^  ^^ 

causing  surface  pressure.  traction  would  be  toward  the  cen- 


FlG 


PURDYj 


QUALITIES   OF   CLAYS    FOR    MAKING    PAVING    BRICK. 


191 


Fig.  17.  Diagram  showing  operation  of  forces 
causing  surface  tension. 


ter  of  the  liquid  mass  as  shown  in  Fig.  17.     This  would  result  in  surface 
tension. 

The  practical  conclusion  from 
the  above  discussion  of  greatest 
interest  in  connection  with  plas- 
ticity, is  that  when  the  surround- 
ing fluid  has  the  greater  poten- 
tiality, flocculation,  or  drawing 
together  of  the  solid  particles 
will  result.  When  the  solid  par- 
ticles have  the  greatest  poten- 
tiality, defiocculation  or  separa- 
tion of  the  solid  particles  will  re- 
sult. Citations  by  the  score 
could  be  presented  showing  that 
clays  can  be  flocculated,  or  de- 
flocculated,  depending  upon  the 
material  carried  in  solution  by 
the  water  used  in  tempering.  It 
is  of  interest,  therefore,  to  consider  the  various  solutions  and  their  ef- 
fect on  clays. 

Solutions  causing  defiocculation — Johnson  in  "How  crops  feed"  cites 
a  great  many  instances  where  solutions  of  organic  compounds  have 
caused  defiocculation  of  soils.  Ackison1  has  shown  that  tannin  will  de- 
flocculate  clay  so  thoroughly  that  when  a  thin  slip  of  clay  suspended  in 
a  solution  of  tamin  is  poured  onto  a  filter  paper  the  water  passing 
through  will  be  very  turbid.  Ammonia  is  used  in  the  water  when  a 
clay  is  being  disintegrated  preparatory  to  mechanical  analyis.  Pe- 
troleum is  greedily  absorbed  by  clay  because  of  its  low  surface  tension 
or  potentiality,  being  held  between  the  minute  grains  of  clay  by  virtue 
of  the  higher  potentiality  of  the  clay  grains.  Whitney1  has  shown  that 
cotton  seed,  meal,  tankage,  etc.,  have  similar  effects. 

It  will  be  important  to  note  that  the  surface  tension  of  solutions 
which  cause  defiocculation  of  grains  of  pure  clay  substance  is  without 
exception  lower  than  the  surface  tension  of  water.  It  will  also  be  impor- 
tant to  note  that  physical  differences  in  conditions  such  as  degree  of 
concentration  of  the  solution,  temperature,  etc.,  that  tend  to  decrease 
surface  tension  affect  defiocculation.  For  example,  it  is  a  common  ex- 
perience of  chemists  that  boiling  for  the  purpose  of  extracting  soluble 
salts  often  so  thoroughly  deflocculates  the  clay  that  even  filtering  through 
a  Gooch  crucible  will  not  clearify  the  filtrate. 

In  the  following  tables  the  surface  tension  of  water  and  of  various 
solutions  is  given. 

1A.  C.  S.,  Vol.  VI,   p.   44. 

2  Bull.  4,  Weather  Bureau,  Dept.  of  Agr.,  p.  17. 


192 


PAVING   BRICK   AND    PAVING    BRICK   CLAYS.  [bull.  no. 

Table  XXII— (1.) 


The  surface  tension  of  water  and  alcohol  in  contact 
with  air. 


Temperature  C° 

Surface  tension 

in  dynes  per  centimeter. 

Water. 

Ethyl  alcohol. 

0° 

75.6 
74.9 
74.2 
73.5 
72.8 
72.1 
71.4 
70.7 
70.0 
69.3 
68.6 
67.8 
67.1 
66.4 
65.7 
65.0 
64.3 
63.6 
62.9 
62.2 
61.5 

23  5 

8 

23.1 
22  6 

10 

15 

22  2 

20 

21  7 

25 

21  3 

30 

20  8 

35 

20  4 

40 

20  0 

45 

19  5 

50 

19  1 

55 

18  6 

60 

18  2 

65 

17  8 

70 

17  3 

75 

16  9 

80 

85 

90 

95 

100 

Table  XXIII  (2). 
Miscellaneous  Liquids  in  Contact  with  Air. 


Liquid. 

Temp.  Cn 

Surface 
tension  in  aynes 
per  centimeter. 

Authority. 

Acetone 

14.0 
17.0 
15.0 
15.0 
15.0 
20.0 
20.0 
20.0 
17.0 

0.0 
68.0 
20.0 
15.0 
20.0 
20.0 

5.8 

97.1 

15.0 

109.8 

21.0 

25.6 
30.2 
24.8 
28.8 
28.7 
30.5 
28.3 
18.4 
63.14 
21.2 
14.2 
470.0 
24.7 
34.7 
25.9 
25.9 
18.0 
29.1 
18.9 
28.5 

Average  of  various. 
.  .do 

Acetic  acid 

Amyl.  alcohol 

..do 

Benzine 

..do 

Butvric  acid 

.  do 

Carbon  disulphide 

Chloroform 

Average  of  various. 
.  .do 

Ether 

Glycerine 

Hall.   . 

Hexane 

Schiff 

Hexane 

.  .do 

Mercury 

Average  of  various. 
.  .do     . 

Methyl  alcohol 

Olive  oil 

.  .do 

Petroleum 

Magie 

Propyl  alcohol 

Schiff 

Propyl  alcohol 

..do 

Tolnol 

..do 

Tolnol 

.  .do 

Turpentine 

Average  of  various. 

1  Smithsonian  physical  tables. 
2 Smithsonian  tables,  Ibid. 


Third  revised  edition,  p.  128. 


PURDY] 


QUALITIES   OF   CLAYS   FOR    MAKING    PAVING    BRICK. 


193 


Table  XXIV  (1). 


Salts  in  Solution. 


Density 


Temp.  C 


Surface  tension  in 
dynes  per  Cm. 


BaCL 

1.2820 
1.0497 
1.3511 
1.2773 
1.1190 
1.0887 
1.0242 
1.1699 
1.1011 
1.0463 
1.2338 
1.1694 
1.0362 
1 . 1932 
1.1074 
1.0360 
1.0758 
1.0535 
1.0281 
1.3114 
1.1204 
1.0567 
1.3575 
1.1576 
1.0400 
1.1329 
1.0605 
1.0283 
1.1263 
1.0466 
1.1775 
1.0276 
1.8278 
1.4453 
1.2636 
1.0744 
1.0360 
1.2744 
1.0680 
1.1119 
1.0329 
1.3981 
1.2830 
1.1039 

15-16 
15-16 

19 

19 

20 

20 

20 

15-16 
15-16 
15-16 
15-16 
15-16 
15-16 

20 

20 

20 

16 

16 

16 
15-16 
15-16 
15-16 
15-16 
15-16 
15-16 
14-15 
14-15 
14-15 

14 

14 
15-16 
15-16 

15 

15 

15 
15-16 
15-16 
15-16 
15-16 
15-16 
15-16 
15-16 
15-16 
15-16 

81.8 

do                                       

77.5 

CaCl 

95.0 

.  .do 

90.2 

HC1 

73.6 

..do 

74.5 

..do 

75.3 

KC1..                   

82.8 

..do 

80.1 

..do 

78.2 

MgCl..                              

90.1 

.  .do 

85.2 

..do...                                             

78.0 

NaCl                                    

85.8 

.  .do 

80.5 

.  .do 

77.6 

NH.C1  

84.3 

.  .do 

81.7 

..do 

78.8 

SrCl,    

85.6 

79.4 

..do 

77.8 

K,CO, 

90.9 

.  .do 

81.8 

..do 

77.5 

NaX03                               

79.3 

77.8 

..do 

77.2 

K  No, 

78.9 

.  .do . . . 

77.6 

CuS04 

78.6 

..do 

77.0 

H,SC>4 

63.0 

..do 

79.7 

..do 

79.7 

K2S04 

78.0 

77.4 

MgS04  : 

83.2 

77.8 

Mn,S04  

79.1 

77  3 

ZnS04 

83.3 

80.7 

..do 

77.8 

Smithsonian  Tables  Ibid. 

Points  to  be  noted  in  table — Notes:  1.  Solution  of  organic  compounds  have  a 
much  lower  surface  tension  than  water.  2.  Surface  tension  decreases  as  the  tem- 
perature increases.  3.  As  the  density  of  the  solution  increases  surface  tension  in- 
creases. 

'    From  the  above  the  following  conclusions  regarding  deflocculation  ap- 
pears : 

1.  It  has  been  shown  that  solutions  of  organic  compounds  cause-  defloc- 
culation. It  is  needless  to  go  into  further  discussion  of  this  point,  for  the 
facts  that  have  been  stated  are  well  understood  by  practical  potters  and  agri-. 
cultural  chemists. 

2.  Increased  temperature  assists  in  producing  deflocculation.  Potters 
who  use  hot  water  in  their  blungers  and  brick  manufacturers  who  use  hot 
water  in  their  pug-mills  have  learned  that  clays  slake  and  develop  plasticity 
more  easily  with  hot  than  with  cold  water.  These  cases  find  their  parallel 
in  the  laboratory  when  clay  slip  is  boiled  in  the  process  of  soluble  salt  de- 
termination.   Deflocculation  is  increased  by  the  use  of  hot  water. 

3.  Increased  density  of  a  deflocculating  solution  does  not  increase  its 
efficiency.  "Ammonia  (1)  has  a  very  marked  action  in  breaking  up  soils 
containing  particles  less  than  0.005  mm.  in  diameter.     .     .     .     One  drop  of 


l  Bull.  No.  24,  Bureau  of  Soils,  U.  S.  Dept.  of  Agr.,  p.  22-24. 


—13  G 


194  PAVING    BRICK    AND    PAVING   BRICK   CLAYS.  [bull.  no.  9 

ammonia  (added  to  5  grams  or  sample  in  50  cc.  of  water)  does  not  seem 
to  be  sufficient  to  break  up  the  flocculations  completely,  but  no  great  change 
is  produced  by  the  addition  of  more  than  5  drops  to  50  cc.  of  watery 
'  The  preceding  facts  given  by  our  foremost  agronomists,  when  consid- 
tered  in  the  light  of  the  fact  that  increased  concentration  of  a  solution 
increases  its  surface  tension,  are  proof  of  the  deduction  that  when  the 
potential  of  the  solid  particles  is  greater  than  that  of  the  surrounding 
fluid,  denocculation  ensues.  In  the  case  of  the  ammonia  solution,  in- 
creased concentration  by  the  addition  of  more  than  5  drops  of  ammonia 
would  so  increase  the  surface  tension  and  consequently  the  potentiality 
of  the  solution  as  the  equalize  the  potentials  of  the  soil  particles  and  the 
solution. 

Solutions  causing  flocculatiou — Having  discussed  the  deflocculating 
solutions  in  detail,  it  will  not  be  necessary  to  dwell  at  length  on  the 
flocculating  solutions,  for  the  effect  on  clay  of  each  class  of  solution  is 
the  converse  of  the  other.  It  is  important  to  note  that  solutions  which 
have  surface  tensions  higher  than  that  of  water  tend  to  cause  floccula- 
tion. 

The  nature  of  solids  affects  flocculation  in  several  ways.  First,  if  the 
clay  or  soil  under  examination  contains  a  large  quantity  of  calcium  or 
magnesium  carbonate1,  it  has  been  found  that  solutions  having  a  surface 
tension  as  low  as  that  of  ammonia  will  cause  flocculation.  Data  are  not 
available  concerning  clay  mixtures  high  in  other  minerals,  but  as  is  about 
to  be  shown,  clays  that  have  comparatively  low  content  of  clay  substance 
probably  have  as  an  average  for  the  several  mineral  grains  a  low  poten- 
tial in  comparison  with  the  potential  of  water.  Clays  high  in  products 
of  decomposition  of  organic  matter  may  be  flocculated  by  ammonia.  In 
fact  the  "potential"  of  the  impure  clays  may  be  so  low  as  to  permit  am- 
monia solutions  to  flocculate  their  grains.  Pure  clays,  i.  e.,  kaolins,  re- 
quire for  their  flocculation  solutions  having  a  "potential"  that  is  higher 
than  that  of  pure  water. 

Second,  near1  the  surface  of  any  soil  there  is  a  concentration  of  solu- 
tions. This  is  adsorption.  If2  the  solid  is  exceedingly  porous,  this  ten- 
dency to  concentration  near  the  surface  is  heightened.  It  is  well  known 
that  salts,  which  are  concentrated  near  the  surface  of  solids  are  precipi- 
tated or  at  least  are  left  clinging  to  the  solids  when  the  water  is  with- 
drawn. Soils3,  even  sand,  possess  the  property  of  attracting  and  fully 
absorbing  salts  which  cannot  be  wholly  washed  out  by  new  quantities  of 
water.  Solutions  of  many  of  the  salts  are  materially  weakened  when 
brought  in  contact  with  solids,  because  of  the  adsorption  of  the  salts,  but 
if -the  surface  of  the  solid  be  relatively  small  no  weakening  of  the  solu- 
tion may  be  perceptible. 

Summary — The  well-known  facts  concerning  a  plastic  clay  when 
wetted  with  water  are,  first,  that  its  finer  portions  are  composed  of  a 
countless  number  of  minute  grains,  the  composition  of  which  has  been 
shown  to  agree  closely  with  that  of  pure  clay  substance ;  second,  that  even 
the  coarser  grains  are  composed  largely  of  kaolinite  and  .other  minerals 

iU.   S.  Dept.   of  Agr.,  Bureau  of  Soils,   Bull.   24,   p.   2  4. 
2U.  S.  Dept.  Agr.,  Rept.  No.  64,  p.  142. 

3  Comp.  Johnson,  How  Crops  Feed.  p.  173. 

4  Comp.  Johnson,  How  Crops  Feed,   p.   334. 


PURDY]  QUALITIES   OF   CLAYS   FOR    MAKING    PAVING    BRICK.  195 

cemented  into  clusters  or  bundles;  third,  that  clays  having  a  high  con- 
tent of  minerals  other  than  kaolin,  are  flocculated  by  solutions  having 
a  surface  tension  lower  than  that  of  water,  while  the  clays  which  are 
practically  pure  kaolinite  in  composition  require  for  their  flocculation 
solutions  that  have  a  surface  tension  higher  than  water;  fourth,  that  clay 
particles  extract  salts  from  solutions  and  hold  them  near  and  on  their 
surface  at  a  high  degree  of  concentration;  fifth,  tlfat  clay  substance  ex- 
hibits this  property  of  adsorbing  salts  to  a  much,  higher  degree  than  any 
of  the  common  anhydrous  minerals,  a  fact  that  makes  the  extreme  fine- 
ness of  the  "clay  sub  stance  in  clays"  of  considerable  significance. 

The  known  facts  concerning  solutions  are :  first,  that  all  solutions  have 
a  surface  tension  which  is  increased  with  increased  concentration;  sec- 
ond, that  those  solutions  which  have  a  surface  tension  higher  than  that  of 
pure  water,  tend  to  cause  flocculation  of  kaolin  grains. 

On  putting  together  the  known  facts  concerning  clay  and  water,  it  is 
evident  that  the  film  of  water  surrounding  the  grains  of  clay,  (when  the 
mass  is  in  a  plastic  condition)  has  a  very  high  potential,  owing  to  the 
high  degree  of  concentration  of  the  salts  that  are  held  to  the  'kaolin  grains 
by  adsorption.' 

SUPPOSED   HISTORY    OF    THE   DEVELOPMENT    OF    PLASTICITY    OF    CLAY'S    IN 

NATURE. 

Daubree1,  Cushman2  and  Mellor3  have  disintegrated  feldspar  in  water 
either  by  grinding  or  by  boiling.  In  all  cases,  the  liquid  in  which  the 
feldspar  was  ground  contained  alkali  in  solution.  Mellor  found  that  not 
only  did  the  solution  give  alkaline  reactions,  but  the  "outlines  (of  the 
solid  particles)  could  be  more  readily  stained  with  saffranine  or  with 
malachite  green  than  before  the  action/' 

Since  the  larger  part  of  the  clay  substance  is  derived  from  the  dis- 
integration of  feldspar,  it  can  be  considered  that  there  was  formed  at 
the  time  of  "kaolinization"  insoluble  hydrous  silicate  of  alumina,  soluble 
potash  salt  and  soluble  silicic  acid.  If  feldspar  has  been  disintegrated 
by  atmospheric  agencies,  water  and  carbonic  acid,  and  the  residual  mass 
is  so  situated  as  not  to  allow  the  soluble  salts  to  be  washed  away,  they 
will  be  retained  in  part  by  adsorption  and  in  part  by  recombination, 
forming  zeolitic  masses.  Data  are  not  available  to  warrant  the  state- 
ment that  plastic  kaolins  formed  in  situ  owe  their  plasticity  to  these  ad- 
sorbed salts,  or  that  they  even  contain  adsorbed  salts.  We  do  know, 
however,  that  nearly  all  kaolins  contain  alkalies  that  can  not  be  shown 
to  be  present  as  constituents  of  such  minerals  as  feldspar  or  mica.  Fur- 
ther we  know  that  "the  less4  free  alkali  a  clay  contains  the  more  will  it 
adsorb."  We  know  also  that  clays  which  have  been  formed  from  feldspar 
under  the  disintegrating  influence  of  fluorine  are  not  plastic,  and  con^ 
tain  fluorspar5  and  other  fluorine  compounds. 

lAm.  Rep.   Smithsonian  Inst.,   1862,   228. 

2U.  S.  Dept.  Asr.,  Bull.  No.  92. 

3Eng\  Cer.   Soc,  Vol.  pt.   1,  p.   72. 

4C.  F.  Binns,   A.   C.   S.,  Vol.  VIII,  p.  206. 

5  Jackson   and   Richardson,    Eng.    Cer.    Soc,   Vol.   II,    p.    59.      (1903-4.) 


196  PAVING   BRICK   AND    PAVING   BRICK   CLAYS.  [bull.  no.  9 

Cushman1  reports  that  the  residue  left  after  disintegrating  the  feldspar 
and  washing  out  the  portions  which  have  been  rendered  soluble,  is  com- 
posed of  very  minute  particles.  If  this  insoluble  portion,  kaolin,  had 
been  formed  by  nature,  in  whose  laboratory  reactions,  precipitations,  etc., 
extend  over  an  almost  infinitely  longer  time  than  is  given  to  similar 
physical-chemical  phenomena  in  the  laboratory,  there  is  no  doubt  but 
that  these  minute  particles  of  kaolin  would  arrange  themselves  in  the 
thin  plate-like  clusters  that  are  characteristic  of  this  substance,  just  as 
did  the  Leasburg  clay  cited  by  Wheeler.  Conditions  will  control  the 
size  of  the  plate-like  crystals  so  developed.  In  many  kaolins  these  plate 
forms  are  discernable,  ranging  from  those  of  sub-microscopic  dimensions 
up  to  those  that  can  be  readily  measured  in  the  microscope.  In  a  clay 
examined  by  the  writer  not  only  were  there  crystals  of  measureable  size, 
but  they  appeared  to  be  compounded,  i.  e.,  made  up  of  several  crystals, 
which  could  not  be  separated  to  an  appreciable  extent  by  vigorous  shak- 
ing in  distilled  water.  Under  natural  conditions,  therefore,  where  the 
disintegrating  water  readily  runs  or  seeps  away,  carrying  the  soluble  por- 
tions and  leaving  the  insoluble  "residual  clay"  in  situ,  we  can  expect  to 
find  a  deposit  that  is  more  or  less  crystalline,  depending  upon  the  attend- 
ing conditions. 

These  deposits,  we  know,  are  practically  non-plastic.  We  know  fur- 
ther from  Ackison's  experiments  and  the  testimony  of  many  agricultural 
chemists,  that  these  grains  can  be  deflocculated  by  organic  solutions. 
Since  surface  waters  generally  contain  organic  substances  in  solution, 
and  since  proximity  of  vegetable  growth  can  give  rise  to  a  deposit  of 
decaying  vegetable  matter  on  kaolin  beds,  it  is  easy  to  see  how  such  a  de- 
flocculation'can  take  place  in  situ,  and  especially  so  if  the  clay  be  moved 
by  running  water  and  deposited  in  the  lower  lands.  By  virtue  of  this 
deflocculation  the  clay  has  a  smoother  feel,  i.  e.,  texture,  and  thereby 
assumes  a  pseudo-plasticity.  This  fact  has  given  rise  to  the  fineness  of 
grain  theory  of  plasticity. 

These  deflocculated  particles  of  kaolin  have,  as  has  been  shown,  a 
high  adsorptive  power.  Whatever  salts  may  be  in  solution  in  the  passing 
waters,  or  may  be  carried  upward  from  lower  strata  by  rising  waters, 
will  be  adsorbed  by  the  kaolin  particles.  Now,  depending  upon  the  de- 
gree of  deflocculation,  amount  of  adsorption,  and  the  kind  of  salt  so  ad- 
sorbed, plasticity  will  be  developed. 

When  non-plastic  kaolins  are  wetted  with  water,  they  are  compressed 
into  shapes  only  with  difficulty,  and  when  dried  they  either  fall  to  pieces, 
as  would  so  much  fine  sand,  or  have  so  weak  a  bond  that  they  are  easily 
crumbled.  The  finer  the  particles,  as  with  the  case  of  sand,  the  more 
readily  can  they  be  shaped  into  pieces  that  will  retain  their  form,  but  no 
matter  how  finely  sub-divided  the  grains  may  be,  the  mass  is  still  very 
friable.  In  this  fine  condition  the  kaolin  no  doubt  possesses  every  chem- 
ical and  physical  property  possessed  by  the  plastic  kaolin  (ball  clay) 
save  that  of  plasticity.  It  has  water  chemically  combined,  molecular 
attraction,  and  adsorbing  properties.     It  becomes  plastic  only  when  it 

1U.   S.  Dept.  Agr.,   Bull.   No.   92. 


PURDY]  QUALITIES   OF   CLAYS    FOR    MAKING    PAVING    BRICK.  197 

has  adsorbed  salts,  the  solution  of  which  exhibits  a  high  surface  tension, 
or  as  Whitney  would  express  it,  which  have  a  relatively  high  potentiality. 
(lavs  having  adsorbed  salts  and  consequently,  plasticity  are  no  longer 
friable  when  molded  but,  on  the  contrary,  they  are  exceedingly  hard. 

It  is  because  of  this  adsorption  property  which  in  kaoline  grains 
seems  to  be  manifested  to  a  higher  degree  than  in  any  other  mineral 
substance,  with  perhaps  the  exception  of  zeolites,  that  many  find  reason 
to  believe  that  plasticity  is  due  to  a  pectoidal  structure  of  the  kaolin 
grains.  Since,  however,  they  cannot  show  that  those  substances  which 
are  known  to  have  a  pectoidal  or  colloidal  structure  can  be  made  t'o 
show  or  develop  plasticity,  and  since  colloids  cannot  be  extracted  from 
plastic  clays,  rendering  them  non-plastic,  nor  added  to  non-plastic 
kaolins  rendering  them  plastic,  we  must  conclude  that  this  theory  is 
hardly  tenable. 

To  what  this  great  adsorptive  power  of  clays  is  due  has  not  as  yet  been 
determined.  We,  however,  must  accept  the  existence  of  this  property 
as  a  proved  fact.  We  must  also  concede  that  when  water  is  added  to  a 
clay,  that  portion  which  envelops  the  very  minute  solid  particles  having 
a  relatively  large  surface  area  in  proportion  to  their  volume,  and  hold- 
ing salts  by  absorption,  will  be  highly  concentrated,  that  the  potential 
of  this  film  will  be  very  much  more  than  those  portions  of  the  water 
farthest  away  from  the  solid  particles;  and  finally,  as  shown  by  the 
flocculation  of  the  clay  particles,  the  potential  of  this  saturated  film 
of  water  is  higher  than  the  potential  of  the  kaolin  particles. 

The  writer  bases  his  assumptions  as  to  the  cause  of  plasticity  on 
known  facts:  Adsorption  of  salts  by  the  kaolin  grains  and  the  con- 
sequent high  potential  of  the  water  film  which  surrounds  the  grains  when 
a  clay  mass  is  in  a  plastic  condition.  On  these  assumptions,  the  cause 
of  the  latent  plasticity  when  clay  is  dry  and  the  developed  plasticity 
when  it  is  wet,  are  obvious. 

Fineness  of  grain,  molecular  attraction,  adsorptive  property,  are 
conditions  that  permit  of  the  adsorption  of  salts.  In  other  words,  they 
are  necessary  conditions. 

METHODS  OF  MEASURING  PLASTICITY. 

General — There  have  been  many  methods  devised  for  measuring 
placticity.  The  methods  suggested  by  Zschokke2  and  Grout3  seem  to 
be  the  most  rational  of  any,  for  in  them  the  resistance  to  deformation 
and  amount  of  flow  before  rupture,  two  characteristic  properties  of 
plastic  bodies,  are  measured.  These  methods  are  based  on  the  same 
principle  as  the  well-known  but  crude  method  of  testing  plasticity  by 
squeezing  a  ball  of  plastic  clay  between  the  tips  of  the  forefinger  and 
thumb,  and  making  a  mental  note  of  the  amount  of  pressure  required 
to  affect  a  given  degree  of  deformation.   . 

The  test  developed  by  this  Survey  involves  the  tensile  strength  of 
the  plastic  mass  rather  than  its  resistance  to  compression,   as  in  the 

1  For  description  of  these  methods  see  "Clays  ;  Occurrence,  Properties  and  Uses" 
by  H.  Ries.     Wiley  and  Sons,  1906. 

2  Thon-Industrie Zeitung-,  No.   120,   p.   1658.      (1905.) 

3W.  Va.  Geol.   Surv.,  Ill,  p.   40. 


198  PAVING   BRICK   AND    PAVING   BRICK   CLAYS.  [bull.  no.  9 

Zschokke  and  Grout  methods.  It  is  believed  that  a  tensile  test  gives 
a  more  accurate  rating  of  the  tenacity  with  which  the  several  grains 
cling  to  one  another,  for  in  this,  friction  between  the  non-plastic  grains 
and  interference  to  fiowage  by  the  larger  ones  crowding  into  one 
another  is  entirely  eliminated. 

Shape  of  the  test  piece — The  special  features  of  the  shape  and  size 
of  the  briquette  employed  in  this  test  are,  first,  narrow  neck,  (%"), 
wide  ends  ( — ")  and  straight  sides  to  fit  the  jaws,  as  explained  later. 
The  smallest  portion  is  cubical  in  shape,  being  %"x%"x%". 

The  clips — In  previous  experiments  it  was  learned  that  the  Standard 
Fairbanks  clips,  using  the  standard  shape  and  size  of  briquette,  would 
permit  the  stretching  of  the  briquettes  until  they  would  slip  out  of  the 
jaws.  Special  clips  were  therefore  made  to  fit  the  briquette.  These 
clips  were  designed  after  Orton1,  differing  from  his  only  in  dimensions, 
angle  of  nip  between  the  jaws,  and  manner  of  adjustment. 

Manufacture  of  briquettes — Clay  was  mixed  to  a  thick  slip,  cast  and 
cut  into  briquettes  by  the  Fox  method,  as  described  under  tensile 
strength.  When  the  cast  slab  had,,  in  the  opinion  of  the  operator,  as- 
sumed its  maximum  plasticity,  the  briquettes  were  cut  and  forced  into 
steel  molds  under  a  constant  pressure  of  fifty  pounds.  This  weight  was 
applied  slowly  but  the  briquette  was  not  allowed  to  remain  under  pres- 
sure after  it  had  received  its  full  load. 

Adjustment  and  calibration  of  the  machines — Before  the  Fairbanks 
machine  could  be  used,  the  balance  beam  had  to  be  poised  to  allow  for 
the  difference  between  the  standard  and  our  special  clips. 

For  measuring  the  stretch  which  the  briquettes  suffered,  the  small 
adjusting  wheel  was  calibrated  so  that  the  peripheral  distance  through 
which  the  wheel  was  turned  would  represent  the  distance  the  under  clip 
had  been  lowered.  The  amount  of  stretch  which  the  briquettes  suf- 
fered at  any  time  during  the  test  was  measured  by  the  fractional  num- 
ber of  turns  of  the  adjusting  wheel  required  to  lower  the  under  jaw 
sufficiently  to  keep  the  beam  in  a  predetermined  position. 

Method  of  procedure — The  plastic  briquette  was  carefully  placed  in 
the  clips  and  the  jaws  adjusted  to  it,  care  being  taken  to  see  that  the 
jaws  on  either  side  were  at  the  same  angle.  The  lower  clips,  suspended 
by  counterpoise,  were  kept  in  a  vertical  line  by  hand  guidance.  Very 
small  shot  was  allowed  to  run  into  the  pail  slowly  until  a  rupture  oc- 
cured  at  the  neck  of  the  briquette.  As  soon  as  a  rupture  occurred,  the 
beam  dropped  with  a  suddenness  that  shut  off  the  flow  of  shot.  At 
the  moment  of  rupture  the  amount  of  initial  stretch  was  noted  by  the 
fractional  number  of  revolutions  through  which  the  adjusting  wheel 
had  been  turned.  Before  removing  the  "load"  the  adjusting  wheel  was 
slowly  turned  until  the  briquettes  was  completely  torn  apart.  The  sec- 
ond peripheral  distance  through  which  the  wheel  had  been  turned  was 
noted  as  "final  stretch." 

The  weight  of  the  shot  required  to  cause  rupture  was  obtained  on  a 
balance  that  is  accurate  to  one  centigram.  While  the  weight  thus  ob- 
tained is  not  the  force  that  was  required  to  cause  rupture,  it  does  bear  a 

lAmer.  Cer.  Soc,  Vol.  VI,  p. 


purdy]  QUALITIES   OF   CLAYS   FOR   MAKING    PAVING   BRICK,  199 

constant  ratio  to  that  force.  The  shot  was  not  weighed  on  the  Fair- 
banks machine  because  it  was  not  sufficiently  sensitive. 

Plasticity  modulus — It  is  obvious  that  since  all  three  factors,  initial 
stretch,  final  stretch,  and  load  required  to  cause  rupture,  must  be  consid- 
ered as  being  affected  by  the  degree  of  plasticity  of  the  clay,  a  modulus 
must  be  devised  that  includes  all  three  factors.  The  one  used  in  our 
tests  was  constructed  as  follows : 

The  central  portion  of  the  briquette  is  a  perfect  cube  %"x%"x%". 
On  the  assumption  that  the  volume  of  this  portion  of  the  briquette  re- 
mains, constant  throughout  the  test1,  and- that  its  cross  section  decreases 
proportionally  as  the  length  increases,  the  decrease  in  cross  section  in 

1.93  (2) 
centimeters  due  to  the  initial  stretch  would  be(    1.92x—        ■   )or  


1.9+ay      1.9+a 

where  a  is  the  initial  stretch.     The  decrease  in  cross  section  after  the 
final  stretch   (here  it  is  figured  as  though  there  has  been  no  rupture) 
X  1.93  1.93\ 

would  be  equal  to  (  ( — ) )  or,  by  reduction, 

\1.9+a  1.9+a+b    J 

1.93b 

where  b  is  the  final  stretch. 

1.92+3.8a+1.9b+a2+ab 

Now  a  measure  of  the  tension  that  is  holding  the  grains  together 
would  be  directly  proportional  to  the  load  and  inversely  proportional  to 
the  decrease  in  cross  section  of  the  briquette  due  to  stretching.  The 
modulus  must,  therefore,  represent  a  value  that  is  directly  as  the  load 
and  inversely  as  the  product  of  the  decreases  in  cross  section  due  to  the 
initial  and  final  stretch.  Performing  this  calculation  and  collecting 
terms  the  following  plasticity  modulus  is  obtained: 

1    (6.859  +  10.83  a  +  3.61  b  +  5.7  a2  +  3.8  ab  +  as  +  a2b)=M 

24.76b 
in  which  L  =  load  in  centigrams,  a  the  initial  stand,  b  the  final  stretch.. 

While  the  modulus  is  very  formidable  looking  it  was  found  that  the 
test  could  be  made  and  the  plasticity  factor  calculated  quite  readily.  In 
fact  the  entire  test  required  less  time  than  did  the  Grout  test  as  carried 
out  in  our  laboratories. 

With  the  heavy  and  far  from  delicate  Fairbanks  machine  and  the 
clumsy  clips,  plasticity  factors  were  obtained  that  varied  for  any  one  clay 
not  more  than  50  per  cent  and  in  some  cases  only  13  per  cent  on  six 
briquettes.  This  percentage  of  variation  was  considered  too  high  to  at- 
tach any  value  to  the  obtained  data,  and  they  are,  therefore,  not  reported. 
It  is  believed  that  with  a  more  delicate  apparatus  this  method  of  measur- 
ing plasticity  would  give  very  close  results  and  that  the  data  obtained 
would  be  a  true  measure  of  plasticity. 

1  This  is  no  doubt  an  incorrect  assumption.  In  iron  they  figure  that  the  length 
increases  four  times  as  much  as  the  cross  section  decreases,  in  other  words  that 
in  the  stretch  the  volume  of  the  test  piece  actually  increases. 

2  The  decrease  in  cross  section  of  the  briquette  is  calculated  instead  of  taking 
the  observed  increase  in  length  because  it  and  the  bond  or  strength  of  the  mass 
are  directly  proportional  while  the  length  is  not. 


200  PAVING    BRICK    AND    PAVING   BRICK   CLAYS.  [bull.  no.  9 

CHEMICAL  PEOPERTIES. 

Value  op  Chemical  Analyses. 

Because,  in  private  correspondence  and  on  every  public  and  semi-public  oc- 
casion that  has  afforded  opportunity,  the  writer  has  taken  a  stand  against  the  large 
absolute  value  and  importance  of  chemical  analysis  of  clays  that  is  contrary  to 
views  popularly  held  by  practical  clay  workers  and  encouraged  by  many  of  the 
State  Survey  reports,  the  discussion  of  the  chemical  properties  of  clays  is  intro- 
duced by  liberal  quotations  from  the  most  eminent  of  ceramic  chemists.  Dr.  Her- 
mann Seger. 

"Thei  demands  which  the  cement  and  the  ceramic  industries  make  on 
the  qualities  of  clay  are  as  different  as  the  purposes  which  these  industries 
pursue. 

"In  the  manufacture  of  Portland  cement  we  have  in  mind  the  obtaining 
of  a  product  of  a  definite  chemical  composition,  and,  since  the  character  of 
clay  as  such  must  completely  vanish  in  this,  the  mutual  relation  of  the  indi- 
vidual constituents  is  to  be  considered  above  all  things,  and  the  physical 
condition  in  which  these  are  found  be  considered  only  as  far  as  it  opposes 
greater  or  less  difficulties  to  the  destruction  of  the  clayey  character. 

"The  clay  industries,  on  the  other  hand,  pursue  a  quite  different  purpose 
in  the  treatment  of  their  raw  material.  The  limits  within  which  the  chem- 
ical constitution  of  clay  may  vary  are  very  wide,  and,  since  the  clayey  char- 
acter of  the  material  is  to  be  preserved,  its  physical  qualities  and  those  of 
its  essential  and  accessory  constituents  are  to  be  placed  in  the  foreground. 
While  for  such  a  purpose,  the  chemical  composition  of  clay,  as  a  whole,  ap- 
pears more  indifferent  and  accidental,  inasmuch  as  it  depends  on  the  mutual 
relation  of  clay,  rock  flour,  sand,  accidental  admixtures  and  their  chemical 
constitution,  the  physical  properties  of  the  same,  the  grain  and  its  form,  cap 
illarity,  plasticity,  fusibility,  etc.,  are  of  greater  importance,  and  the  chemi- 
cal constitution  of  each  of  these  constituents  is  to  be  considered  only  as  far 
as  it  permits  us  to  infer  the  physical  properties  of  the  whole.  It  is  surely 
a  serious  mistake  to  treat  material  so  heterogeneous  chemically  and  me- 
chanically, as  the  clays  and  earths  used  in  the  ceramic  industries,  like  sub- 
stances chemically  and  physically  homogeneous,  as  for  example  glass,  and  to 
base  conclusions  with  regard  to  their  properties  on  their  chemical  composi- 
tion. 

"The  chemical  changes  which  the  materials  of  the  ceramic  industries 
suffer  in  the  course  of  manufacture,  step  into  the  background,  with  the 
exception  of  the  loss  of  chemically  bound  water,  which  has  as  a  consequence 
the  loss  of  plasticity,  and  must  not  be  produced  in  the  same  degree  as  in 
the  manufacture  of  cement  and  glass,  or  the  material  will  lose  its  earthy 
character.  In  fact,  it  seems  advisable  to  drop  the  investigation  of  the  chem- 
ical composition  of  clay  as  a  whole,  and  put  in  its  place  a  deeper  study  of 
the  composition  of  the  essential  and  accidental  constituents,  in  order  to 
to  infer  the  properties  of  the  whole  from  the  properties  of  the  compounds 
thus  obtained.  For  example,  we  need  not  ask  how  much  pure  clay  and 
silicic  acid  we  have  in  clay,  but  what  part  of  the  clay  and  silicic  acid  be- 
longs to  the  sandy  constituents,  what  part  to  the  silty,  or  the  clayey  con- 
stituent, and  what  physical  properties  must  we,  according  to  these  data, 
ascribe  to  the  sand,  rock  dust,  clay,  etc.,  individually. 

"It  cannot  be  denied  that  in  the  examinations  of  clays  scrupulously  accur- 
ate analyses  of  the  material  have  heretofore  been  made,  but  that  little  has 
been  learned  concerning  structure,  condition  of  plasticity,  power  of  absorbing 
water,  shrinkage  on  drying  and  burning,  form  and  size  of  grains  of  sand, 
and  rock  dust,  concerning  the  pecularities  of  the  concretions,  and  concern- 
ing efflorescences  and  incrustations.  In  the  consideration  of  the  properties 
of  clay  for  the  purposes  of  the  clay  industries  we  must  put  ourselves  more 
upon  a  physical  than  a  chemical  standpoint. 


l  Dr.  Hermann  Segar,  the  Collected  Writings  of,  Trans,  by  A.  C.  S.  p.  8-11. 


PURDY]  QUALITIES   OF   CLAYS    FOR    MAKING    PAVING    BRICK.  201 

"Ifi  chemical  analysis  has  discovered  a  fixed  relation  between  alumina, 
silicic  acid  and  flux,  we  know  that  these  constituents  belong  essentially  to 
a  single  well-characterized  combination,  so  that  we  can  take  the  degree  of 
refractioriness  from  the  laws  established  by  Bischofand  Ritchers  with  a 
greater  or  less  assurance,  according  as  this  substance  is  present  in  a  greater 
.or  less  degree  of  purity.  However,  if  we  should  proceed  in  a  similar  way 
in  the  investigation  of  brick  clays,  we  would  get  a  theoretical  result  so 
very  different  from  the  practical  results  that  it  would  have  no  value  what- 
ever in  regard  to  the  knowledge  of  the  material.  The  chemical  analysis 
gives  us  only  an  average  of  the  composition  of  the  components  forming  the 
clay,  differing  very  widely  in  their  chemical  composition  and  their  physi- 
cal properties.  Since  the  clay,  after  burning,  preserves  its  earthy  charac- 
ter, and  the  various  constituents  act  only  superficially  on  each  other,  the 
chemical  analysis  gives  us  absolutely  no  clue  for  the  deduction  of  definite 
properties  of  the  whole. 

"Tico  bri\ck  clays  may  have  exactly  the  same  composition  and  still  differ 
in  every  respect,  because  the  complete  analysis,  for  example,  gives  us  no 
idea  whatever  as  to  how  much  silicic  acid,  alumina  and  flux  belong  to  the 
clay  substance,  to  the  rock  dust,  and  to  the  sand  individually;  for  instance, 
in  the  one  case  all  or  the  greater  part  of  the  flux  may  belong  to  the  clay 
substance,  in  another  case  to  the  constituents  which  make  clays  lean,  and 
accordingly  the  properties  of  the  compound  be  subject  to  the  greatest  varia- 
tion with  the  same  percentage  composition.  In  the  one  case  it  may  be  the 
clay,  in  another  the  rock  dust  or  s.and,  which,  with  the  same  percentage 
composition  of  the  whole,  is  the  most  fusible  constituent,  as  admixed  iron 
oxide  or  carbonate  of  lime,  which  according  to  the  manner  of  distribution 
are  inclined  to  have  the  strongest  effect  sometimes  on  the  clay,  sometimes 
on  the  rock  dust  and  sand,  and  thereby  produce  a  number  of  variations 
which  find  not  the  slighest  explanation  by  a  simple  chemical  analysis. 

"If  we  conclude  from  this  that  chemical  analysis  can  claim  only  a  limited 
value  for  the  discovery  of  the  properties  of  brick  clay,  such  a  judgment 
would  be  highly  one-sided  and  inaccurate.  .  .  .  For  our  purpose  it  is 
especially  the  physical  properties  of  clay  that  are  of  greatest  importance  in- 
judging  the  same,  and  the  chemical  properties  only  as  far  as  they  supple- 
ment the  former.  Here,  therefore,  to  express  it  in  a  few  words,  it  will  be 
the  task  of  the  chemical  analyst  to  determine  the  composition  of  the  con- 
stituents that  are  physically  alike,  that  of  the  clay,  rock  dust,  sand,  and 
accessory  constituents,  separately  and  singly,  and  to  make  possible  a  com- 
parison of  these  with  each  other.  In  this  way  we  are  able  to  get  a  good 
idea  of  the  properties  of  the  components,!  whereas  an  analysis  of  the  whole 
mass  would  be  of  little  use.  We  are  thus  convinced  of  the  necessity  of 
physical  analysis  of  clay  simultaneously  with,  or  rather  before  the  chemical, 
as  far  as  the  investigation  is  made  for  the  purposes  of  pottery  ware,  and 
especially  for  the  manufacture  of  bricks.  Even  though  scientific  men  have 
repeatedly  referred  to  the  importance  of  the  mechanical  and  physical  inves- 
tigations, this  direction  of  the  investigation  has  not  been  pursued  with  such 
vigor  that  the  results  obtained  from  it  show  any  real  use  for  the  brick 
industry." 

In  the  foregoing  statements  Dr.  Seger  has  very  forcibly  set  forth  the 
same  doctrines  that  the  writer  has  come  to  thoroughly  believe  as  a  re- 
sult of  observations  in  the  factory  and  laboratory.  In  subsequent  writ- 
ings Dr.  Seger  set  forth  the  value  of  what  is  known  as  the  "Eational 
analysis"  in  which  "clay  substance/'  feldspar  and  free  silica  are  differ- 
entiated. He  cited  many  case's  in  which,  with  the  aid  of  the  Eational 
analysis,  he  was  able  to  obtain  more  clearly  an  idea  of  the  constitution 

1  Seger,  loc.  cit,  p.  36. 

2  Italics  not  in  the  original. 

3  Italics  not  in  the  original. 

4  Italics  not  in  the  original. 


202  PAVING   BRICK    AND    PAVING    BRICK   CLAYS.  [bull.  no.  9 

and  properties  of  clay  than  he  could  from  any  other  method  of  analysis. 
In  this,  however,  he  was  no  doubt  over  zealous,  for  later  studies  by  other 
chemists  proved  that  not  only  does  the  "Kational  analysis"  fail  to 
sharply  differentiate  between  the  "clay  substance,"  feldspar  and  free 
silica,  but  that  the  analysis  is  of  value  only  in  the  purest  clays,  viz. : 
China  and  ball  clays.  The  writer  has  made  'rational"  analysis  of  many 
types  of  clays,  and,  barring  those  used  in  the  vitreous  pottery  wares,  he 
is  compelled  to  state  that  not  once  has  he  been  able  to  obtain  a  clearer 
insight  into  the  actual  constitution  of  the  clays  than  he  could  from  the 
gross  or  ultimate  analyses.  Predictions  concerning  a  clay  based  on  a 
rational  analysis  in  the  great  majority  of  cases,  go  very  far  wrong. 
After  considerable  pains  and  labor  in  the  execution  of  the  analysis  the 
operator  is  compelled  to  make  guesses  that  are  much  less  scientific  and 
accurate  than  he  would  if  he  had  merely  burned  a  piece  of  the  same  clay 
in  a  small  muffle  furnace,  and  noted  the  rate  of  change  in  color  and  dem- 
sity  with  increasing  intensity  of  heat  treatment,  a  test  that  ought  not 
to  require  more  than  three  hours  time,  and  can  be  made  by  any  one  who 
has  access  to  a  kiln. 

It  was  shown  in  a  preliminary  report  on  the  fire  clays  of  Illinois1 
that  fire  clays  having  the  same  ultimate  chemical  composition  behave 
very  differently  in  burning.  Indeed  the  chemical  composition  and  ulti- 
mate fusion  period  were  very  often  found  to  coincide  in  clays  which, 
on  the  one  hand,  would  remain  open  and  porous  through  sufficiently 
long  and  severe  heat  treatments  to  make  them  fit  for  use  in  fire  brick, 
or,  on  the  other,  would  be  nearly  vitrified  under  the  heat  treatment  used 
in  burning  stoneware  and  sewer  pipe.  Such  phenomena  are  discussed 
and  illustrated  in  this  report  under  the  title  of  pyro-physical  and  chem- 
ical properties  of  clays. 

In  the  manufacture  of  vitreous  floor  tile  the  writer  learned  by  prac- 
tical experience  that  particular  effects  either  in  color,  vitreousness,  ulti- 
mate fusibility,  or  any  other  physical  property  requisite  in  the  produc- 
tion of  floor  tile,  could  not  be  duplicated  on  the  basis  of  chemical  com- 
position. 

This  was  also  found  true  in  the  manufacture  of  porous  white  ware 
bodies,  such  as  are  used  in  jardinieres  and  art  wares,  and  no  doubt  is  en- 
tertained but  that  the  same  would  be  found  to  hold  true  to  a  large  ex- 
tent in  the  manufacture  of  vitreous  china.  In  these  cases,  however, 
rational  analysis,  i.  e.,  the  determination  of  the  proportional  quantity 
of  clay  substance,  feldspar,  and  free  silica  finds  value  in  that  these  sev- 
eral minerals  have  decided  effect  on  the  expansion  and  contraction  of 
the  blended  pottery  body,  and,  consequently,  upon  the  proper  fitting 
on  it  of  a  glassy  coating  (the  glaze.) 

The  only  instance  in  which  chemical  analysis  is  of  positive  aid,  aside 
from  the  explaining  of  some  "observed  phenomenon,  is  in  the  execution 
and  study  of  a  systematically  planned  series  of  experiments.  Seger's 
classical  studies  that  resulted  in  the  invention  of  the  pyrometric  cones 
would  probably  never  have  been  carried  out  had  he  not  followed  closely 

1  Purdy  and  De  Wolf,   Preliminary  Report  on  the  Fire   Clays  of  Illinois,   State 
Geol.   Surv.  of  111.     Year-book  1906,  pp.   137. 


PURDYl  QUALITIES   OF   CLAYS    FOR    MAKING    PAVING    BRICK.  203 

the  chemical  analyses  of  the  raw  materials-  and  planned  his  series  on 
chemical  formulae.  Following  him,  there  has  been  much  of  exceedingly 
great  value  resulting  from  researches  in  pottery  mixtures  that  would 
have  been  impossible  on  any  other  than  a  strictly  chemical  basis.  In  the 
study  of  paving  brick  clays  here  reported  the  fact  has  been  discovered 
that  the  best  paving  clays  contain  a  relatively  high  content  of  magnesia. 
Such  a  discovery  has  been  and  would  have  been  impossible  from  an 
analysis  of  an  isolated  sample.  Further,  this  fact  would  not  have  been 
noted  had  no  systematic  researches  on  a  chemical  basis  been  made  with 
pure  clays,  minerals,  and  magnesia  compounds,  showing  that  mixtures 
containing  a  comparatively  high  content  of  magnesia  have  a  long  fusion 
range,  for,  as  will  be  seen  later,  the  value  of  clays  for  paving  brick  man- 
ufacture, or  even  their  fusion  range,  do  not  always  correlate  with  high 
magnesia  content. 

The  suggestion  made  by  Dr.  Seger  in  the  paragraphs  quoted  in  the 
introduction  to  this  chapter,  that  a  chemical  analysis  of  the  several  sub- 
divisions of  the  particles  according  to  size  would  be  of  value,  is  possibly 
true.  In  fact  it  is  obvious  why  such  should  be  the  case.  The  time  and 
trouble  involved  in  making  a  thorough  mechanical  analysis  of  a  clay  into 
several  groups  having  different  ranges  in  size  of  particles  in  quantities 
sufficient  to  make  accurate  and  especially  duplicated  analyses  of  each 
group,  places  such  a  determination  out  of  consideration  as  a  commercial 
test  on  clays.  But  for  a  scientific  purpose  it  is  believed  that  the  re- 
sults obtained  would  justify  the  expense  and  trouble  involved.  Such  a 
study  was  made  by  Grout  on  a  composite  sample  of  West  .Virginia  clays. 
His  results  are  cited  and  discussed  on  pages  179  to  180  of  this  report. 
So  far  as  the  writer  is  aware,  Grout  was  the  first  to  make  such  an  analy- 
sis, and  it  is  hoped  that  the  deductions  drawn  from  his  results  show 
justification  for  the  making  of  similar  studies  on  single  clays. 

Notwithstanding  the  fact  that  up  to  date  it  would  be  but  a  matter 
of  chance  that  an  interpretation  of  the  results  of  a  chemical  analysis 
would  agree  with  the  observed  working  properties  of  a  clay,  it  should 
not  be  concluded  that  our  chemists  may  not  in  the  near  future  devise 
a  method  of  analysis  that  will  meet  the  requirements  of  the  case.  In 
fact,  so  strongly  do  many  believe  that  this  will  come  to  pass,  that  they 
•  see  justification  in  making  and  reporting  chemical  analyses  of  clays  by 
geological  surveys,  as  has  been  their  wont  in  the  past.  The  writer  firmly 
believes,  however,  that  as  a  forerunner  to  such  an  event,  many  carefully 
executed  and  systematic  physical  and  chemical  researches  on  each  type 
of  clay  must  be  made  with  parallel  observations  on  synthetical  mixtures 
of  pure  minerals.  A  few  such  observations  will  be  made  in  subsequent 
paragraphs. 

MlNERALOGICAL  COMPOSITION  OF   CLAYS. 

Clay  is  a  heterogeneous  aggregation  of  minerals  in  which  kaolin  is 
present  in  sufficient  quantities  to  give  to  the  mass  its  characteristic 
physical  properties.     If  kaolin  is  not  present  in  sufficient  quantities. to 


204  PAVING   BRICK    AND    PAVING    BRICK   CLAYS.  [bull.  no.  9 

do  this  the  mass  should  uot.be  called  clay.  If  limestone  contains  some 
kaolin  entrapped  mechanically,  the  mass  is  a  limestone,  notwithstanding 
the  fact  that  it  contains  a  considerable  quantity  of  kaolin,  for  it  looks 
and  behaves  in  every  way  like  limestone.  But  if  the  lime  should  be 
dissolved,  as  we  know  has  often  been  the  case,  until  the  material  is  lar- 
gely  composed  of  kaolin,  this  residual  mass  is  clay. 

There  is  a  commercial  modification  of  this  definition  that  involves 
its  economic  use  or  value.  For  instance,  if  the  mass  should  contain 
iron  in  sufficient  quantities  to  render  it  a  commercial  source  of  iron, 
the  mass  is  more  properly  called  an  iron  ore,  just  as  a  limestone  impreg- 
nated with  zinc  or  lead  is  termed  a  zinc  or  lead  ore.  Aside  from  cera- 
mic consideration,  a  clay  containing  iron  or  any  other  substance  of  com- 
mercial value  in  sufficient  quantities  to  allow  of  its  being  considered  a 
source  of  that  substance  from  a  commercial  standpoint  would  be  con- 
sidered an  ore. 

COMPLEXITY   OF   M1NERALOGICAL   COMPOSITION   OF    CLAY. 

In  the  section,  the  "geology  of  clays,"  Professor  Eolf e  has  set  forth 
in  detail  the  most  accepted  -theory  of  the  origin  of  clays,  the  effective 
agencies  of  rock  decomposition,  and  the  manner  in  which  these  agencies 
operate.  It  has  been  shown  clearly  that  the  residual  mass  resulting 
from  rock  decomposition  may  be  comprised  of  a  variety  of  silicates,  the 
kind  and  number  of  silicates  formed  being  dependent  upon  the  con- 
ditions attending  the  rock  decomposition.  Professor  Cook,1  after  giving 
the  analyses  ef- several  of  the  New  Jersey  kaolins  that  differ  widely  in 
chemical  composition,  remarks : 

"The  examples  above  stated  prove  conclusively  that  clays  are  not 
altogether  uniform  in  composition,  even  after  throwing  out  all  the  ac- 
cidental or  foreign  constitutents.  Either  the  essential  kaolinite  is  not 
constant,  or  our  clays  consist  of  this  mineral  mixed  in  varying  propor- 
tions with  other  hydrous  silicates  of  alumina.  Inasmuch  as  the  greater 
number  of  the  rich  fire  and  ware  clays  of  the  State,  and  also  others* 
which  have  been  here  era  mined,  d.o  correspond  very  closely  to  the  com- 
position and  formula  assigned  to  this  mineral,  the  latter  explanation  is 
more  plausible." 

After  nearly  thirty  years  of  constant  research  Dr.  Cook's  problem 
is  no  nearer  solution,  for  Dr.  Clark  in  Bull.  125  of  the  U.  S.  Geological 
Survey,  suggests  that  there  are  seven  possible  combinations  of  alumina, 
silica  and  water  of  combination,  which  might  form  crystalized  kaolin. 

Professor  Eolfe  has  shown  that  a  pure  kaolin  can  be  formed  only  by 
the  decomposition  of  rocks  that  consist  almost  altogether  of  feldspathic 
or  other  highly  aluminous  minerals,  together  with  comparatively  tmde- 
composed  minerals  like  quartz  and  mica,  that  are  in  large  part  separ- 
able from  the  kaolinite  grains  by  elutriation.  If  the  parent  rock  con- 
tains iron  or  other  metallic  oxide  bearing  minerals  the  residual  kaolin 
will  be  contaminated  with  these  coloring  oxides  in  such  a  manner  as  to 
render  its  purification  by  elutriation  impossible.  If  it  is  impossible  to 
determine  the  mineralogical  constitution  or  makeup  in  the  former  case, 

l  Report  on  the   Clay  Deposits  of  New  Jersey,   Geol.    Surv.   of  N.   J.   1878,   pp. 
269-272. 


PURDY]  QUALITIES   OF   CLAYS    FOR    MAKING    PAVING   BRICK.  205 

where  the  residual  deposit  is  largely!  pure  kaolin,  contaminated  only 
with  substances  that  are  separable  in  running  water,  it  is  obvious  that  in 
the  latter  case,  that  of  the  impure  deposit,  the  problem  is  far  more  com- 
plicated. 

The  difficulty  of  determining  the  mineralogical  composition  of  a  clay 
is  increased  many  fold  in  the  case  of  those  that  have  been  transported 
from  the  place  of  origin  and  contaminated  with  a  heterogeneous  as- 
sortment of  inorganic  materials  encountered  en  route.  Shales  may 
vary  so  widely  in  their  mineralogical  constitution  that  in  one  case  the 
mass  may  be  highly  ferruginous,  in  another  nighly  calcareous,  and  so 
on,  depending  upon  the  amount  and  kind  of  contaminating  substance. 
Because  the  shale  is  highly  calcareous  it  does  not  follow  that  it  is  a  simple 
mixture  of  calcium  carbonate  and  kaolin,  but  rather  that  the  predomin- 
ant adulterant  is  calcium  carbonate.  Silica,  iron  compounds,  etc.,  may 
be  and  usually  are  present  in  considerable  quantities  in  the  calcareous 
shales.  The  nearest  that  geologists  or  ceramists  have  come  to  deter- 
mining what  inorganic  substances  are  present  in  a  given  shale,  is  sim- 
ply to  say  that  it  is  calcareous  or  silicious,  etc.  It  has  not  been  found 
possible  to  determine  the  mineralogical  composition  of  any  of  the  com- 
plex secondary  clays  either  by  the  microscope  or  by  chemical  analysis 
Approximation  to  the  mineralogical  composition  of  the  purer  secondary 
clays  like  the  ball  clays,  is  made  possible  by  "rational  analysis,"  in 
which  the  differentiation  of  the  minerals  depends  upon  their  relative 
solubility  in  sulphuric  acid,  yet  by  this  method  it  is  incorrectly  assumed 
that  only  three  mineral  components  are  present,  i.  e.,  clay  substance, 
feldspar,  and  quartz,  and  the  results  are  forced  to  tally  with  this  as- 
sumption. 

It  is  obvious,  therefore,  that  an  attempt  to  distinguish  the  minerals 
that  occur  commonly  in  clays  would  be  useless  in  discussing  the  min- 
eralogical composition  of  clays  in  general,  and  much  more  so  in  the  case 
of  any  particular  clay. 

Granted  that  it  would  be  possible  to  make  a  fairly  accurate  mineral- 
ogical analysis  of  a  clay,  it  is  doubtful  if  our  present  knowledge  would 
enable  us  to  predict  its  working  qualtities  or  even  its  fusibility  with 
accuracy.  When  it  is  considered  that  a  mixture  of  40  per  cent  quartz 
and  60  per  cent  feldspar  has  approximately  the  same  pyrometric  value 
as  feldspar  taken  alone,  and  that  both  have  like  effect  on  the  green  prop- 
erties of  clay,  some  idea  of  the  complexity  of  the  problem  is  apparent. 
\\  hat  is  true  of  a  mixture  of  feldspar  and  flint  is  true  of  a  large  number 
of  pairs  of  other  minerals.  What  is  true  of  minerals  when  considered 
in  pairs,  is  true  to  a  larger  degree  when  taken  in  a  multiple  combin- 
ation. It  does  not  require  much  imagination  to  see  where  one  would  be 
led  if  it  should  be  required  to  predict  the  fusion  behavior  or  a  hetero- 
geneous mixture  of  a  large  number  of  minerals. 

This  sort  of  a  study  is  of  value  and  in  fact  is  now  looked  upon  as  a 
necessity  in  the  compounding  of  artificial  mixtures  of  clays  and  min- 
erals for  pottery  purposes,  but  in  these  cases  the   operator  is  dealing 


206  PAVING    BRICK    AND    PAVING   BRICK   CLAYS.  [bull.  no.  9 

with  substances  the  mineral  character  of  which  is  to  a  large  degree 
known,  and  he  is  mixing  these  minerals  in  predetermined  proportions. 
He  has  in  this  case  a  synthetical  mixture  of  known  mineralogical  con- 
stitution adn  of  comparative  simplicity  (containing  at  the  most  not 
more  than  four  or  five  different  minerals,  and,  therefore,  his  practical 
experience  ought  to  enable  him  to  predict  its  physical  and  pyro-chem- 
ical  behavior.  In  the  case  of  nature's  mixtures,  however,  man  has  at 
present  no  way  of  determining  their  mineralogical  constitution,  and 
must  depend  upon  an  actual  test  for  obtaining  a  knowledge  of  the 
working  properties  of  the  mixture. 

To  illustrate  these  difficulties  reference  might  be  made  to  the  fire 
clays,  which  are  comparatively  pure  clay  substance  or  at  least  rela- 
tively simple  mixtures  of  mineral  ingredients.  It  has  been  shown1  that 
in  plotting  the  position  that  indicates  the  relative  fusibility  of  the  clays 
on  the  basis  of  their  alumina-silica  ratio  in  reference  to  the  position  oc- 
cupied by  a  synthetical  mixture  having  a  similar  alumina-silica  ratio, 
no  concordant  relation  existed  between  them.  Further  the  difference 
between  the  No.  1  and  the  No.  2  fire  clays  of  the  usual  clay  workers7 
classification  having  practically  the  same  ultimate  fusion  point,  but 
differing  from  one  another  in  the  manner  of  vitrification  is  no  doubt 
explainable  either  on  account  of  difference  in  mineralogical  composi- 
tion or  character  of  grains.  What  is  true  in  the  case  of  simple  mineral 
mixtures  like  the  fire  clays  would  be  greatly  exaggerated  in  the  case  .of 
the  exceedingly  complex  mixtures,  such  as  most  of  the  shales  and  sur- 
face clays. 

Ultimate  Chemical  Composition. 

By  ultimate  chemical  composition  is  meant  the  percentage  by  weight 
of  the  several  oxides  of  the  elements  that  occur  in  clay  irrespective  of 
their  original  state  or  combination.  Ordinary  chemical  analyses  are  re- 
ported in  terms  of  so  much  silican  oxide,  aluminium  oxide,  calcium 
oxide,  etc.  All  are  more  or  less  familiar  with  such  analyses,  and  not  a 
few  brick  manufacturers  have  had  repeated  analyses  of  their  clays  made 
by  chemists.  The  reports  they  received  are  what  is  known  as  the 
"Ultimate  Chemical  Analysis/'  in  contradistinction  to  the  rational 
analysis,  that  gives  the  supposed  approximate  percentage  of  clay  sub- 
stance, feldspar  and  quartz  in  the  clay,  instead  of  the  individual  ox- 
ides of  which  these  substances  are  composed. 

The  persistent  belief  in  the  value  of  an  ultimate  chemical  analysis 
on  the  part  of  layman  and  scientist  alike  is  a  not  wholly  unwarranted 
compliment  to  the  science  of  chemistry.  It  cannot  be  denied  that  there 
is  some  slight  foundation  for  this  unflinching  confidence  in  the  value 
of  an  ultimate  chemical  analysis,  but  it  is  equally  true  that  even  after 
these  many  years  of  constant  research  by  scientists  the  world  over,  very 
little  advance  has  been  made  in  ability  to  interpret  the  facts  that  ought 

l  Preliminary  Report  on  Fire  Clays,  State  Geol.   Surv.,  Bull.  4,  p.   138. 


purdyJ  QUALITIES   OF   CLAYS   FOR    MAKING    PAVING   BRICK. 


207 


to  be  disclosed  by  such  analyses.  Because  so  many  chemists,  as  well 
as  laymen,  do  not  seem  to  understand  the  difficulties  that  attend  the 
interpretation  of  such  an  analysis,  a  brief  review  of  a  few  of  the 
recorded  facts  will  be  given. 

In  1868.  Eichters1  in  his  classic  work  entitled  "Eefractoriness  of 
Clays,"  promulgated  laws  in  regard  to  the  fluxing  effect  of  the  various 
elements  in  simple  mixtures  at  high  heats  that  are  now  known  as  the 
Eichters  laws.  In  1895,  E.  Cramer  published  in  the  "Thon-Industrie 
Zeitung"  a  review  of  Eichter's  work  confirming  his  laws  in  every  re- 
spect. The  fluxing  behavior  of  the  various  bases  according-  to  Eichter's 
laws  are  shown  "in  the  following  curves.     Figs.  18  to  21. 


NanO 


FIG.  18.  Diagram  showing  operations  of  fluxes  in  kaolin,  using  equal  parts  of  each.     (Ex- 
ample. kaolin=98^',  K^O^i.) 


1  From  lecture  notes  by  Prof.  Edward  Orton,  Jr. 


208 


PAVING   BRICK   AND    PAVING   BRICK   CLAYS.  [bull.  no.  9 


K20  Na2Q  CaO  MgO  FeO 


0.15 


Fig.  19.  Diagram  showing  operation  of  fluxes  in    kaolin  using  fractions  of   their  atomic 
weights.     (Example;  Al.,032SiOo=222. 8  at.  wt.    K20  94.22  mol.  wt.    K30  mixture=222.8+ 


94.22 
20 


,  1st  vertical  line. 


purdyJ  QUALITIES   OF   CLAYS    FOE    MAKING    PAVING    BBICK. 


20» 


K20  Na20  CaO'  MgO  FtO 


Fig.  20.  Diagram  showing  operation  of  fluxes  on  Al203+2Si02+^Si02   mixtures  using 

equal  weights  of  each. 


—14  G 


210 


PAVING   BRICK   AND    PAVING   BRICK   CLAYS.  Ibull.  no.  9 

K20  Na20  CaO  MgO  FtO 


F  F.  21.  Diagram  showing  the  result  of  Kichter's  investigation  of  various  oxides. 

From  Eichters7  and  Cramer's  investigations  it  is  learned  that  the 
order  of  fusibility  of  the  different  oxides  in  simple  clay  mixtures  is  as 
shown  in  the  first  column  of  the  following  table.  In  the  presence  of 
free  silica  the  order  is  changed  somewhat,  as  is  shown  by  contrasting- 
the  order  given  in  the  third  column  with  that  given  in  the  first.  Go- 
ing to  the  other  extreme  of  silicate  mixture,  that  of  glazes,  the  order  of 
the  fluxing  effect  of  the  various  oxides  is,  according  to  Seger1  as  given 
in  the  fifth  column. 

Seger  further  says:  "The  law  established  by  Eichter  and  Bischof, 
concerning  the  fusibility  of  clays,  'that  equivalent  proportions  of  fluxes 
exert  an  equal  influence  on  the  fusibility/  and  which  appears  to  be  ap- 

i  Seger' s  collected  works.     Vol.  2,  A.  C.  S.  Translatun,  p.  568. 


PURDY] 


QUALITIES   OF   CLAYS    FOR    MAKING    PAVING    BRICK. 


211 


Table  XXV. 
Showing-  fluxing;  behavior  of  the  various  oxides  in- 


Pure  Kaolin. 

Kaolin+J^  mol.  flint. 

Glazes. 

Oxide. 

Molecular 
weight. 

Oxides. 

Molecular 
weight. 

Oxides. 

Molecular 
weight. 

40 
56 
72 
62 
94 

Magnesia.. 

Iron 

Calcium. .. 

Soda 

Potash  .... 

49 
72 
56 
62 
94 

Lead 

Barium.. .. 
Potash  .... 

Soda 

Zinc 

Lime 

Magesia... 
Alumina... 

222 

153 

Iron 

94 

62 

Potash 

81 

56 

40 

102 

proximately  correct  for  the  very  high  temperatures  employed  in  clay 
testing,  and  for  the  very  small  quantities  of  the  fluxes  coming  into  ac- 
tion in  the-  clays,  has  no  bearing  on  the  glasses  and  glazes,  far  richer  in 
fluxes  and  melting  at  far  lower  temperatures." 

Ludwig1  having  made  similar  studies  with  more  complex  mixtures 
summarizes  his  results  as  follows : 

"First — Richters'  law  is  a  special  case  of  the  general  law  of  dilute  solu- 
tions. 

Second — This  law  is  restricted  by  the  following  correlations: 

a.  It  applies  only  to  very  dilute  solutions,  that  is,  clays  with  a  small 
amount  of  fluxes  and  not  to  brick  clays  or  glazes. 

b.  Is  assumes  intimate  mixtures. 

c.  Iron  shows  a  different  effect,  due  to  its  two  stages  of  oxidation,  since 
one  molecule  of  ferric  oxide  corresponds  to  two  molecules  of  ferrous  oxide. 
A  given  percentage  of  iron  contains  fewer  molecules  of  ferric  oxide  than 
of  ferrous  oxide,  since  the  former  has  a  higher  molecular  weight.  On 
changing  to  the  ferrous  oxide  the  number  of  molecules  is  doubled,  and 
hence  the  fluxing  action  is  doubled. 

Third.  The  analysis  of  a  fire  clay  is  of  great  importance  in  estimating 
its  refractioriness. 

Fourth.  The  estimation  of  refractioriness  by  means  of  the  percentage  of 
alumina  and  fluxes  leads  to  erroneous  results." 

From  the  above  citation  it  must  be  concluded  that  the  fluxing  power 
of  a  given  oxide  is  affected  very  materially  by  the  kind  and  number  of 
oxides  present,  as  well  as  their  chemical  combination,  degree  of  hydra- 
tion, oxidation,  etc.  The  facts  gleaned  from  a  study  of  the  fluxing 
effect  of  a  single  oxide  in  a  simple  mixture  do  not  necessarily  hold 
true  in  the  same  degree  in  complex  mixtures.  It  is  well  known  in 
glaze  manufacture,  for  instance,  that  a  mixture  of  several  fluxes  pro- 
vokes greater  fusibility  than  a  mixture  of  any  two  or  them.  What  is 
true  of  glazes  is  likewise  true  of  clays. 

The  difficulty  of  interpreting  the  results  of  chemical  analyses  is  more 
largely  due  to  a  lack  of  experimental  evidence  on  the  fluxing  behavior 
of  known   complex  mixtures.     Interpretation   of  the   facts   concerning 

l  Thon-Industrie  Zeitung,  Vol.  XXVIII,  p.  773,   1904.     Abstracted  by  Bleininger, 
A.  C.  S.,  p.  275.     Trans.  VII,  p.   275.  1905. 


212 


PAVING   BRICK   AND    PAVING    BRICK   CLAYS.  [bull.  no.  9 


a  given  mixture  is  impossible  until  there  is  more  known  about  mixtures 
of  the  same  component  substances  in  different  proportional  combina- 
tions. For  example,  Seger1  has  shown  that  the  fusibility  of  mixtures 
of  pure  AbO  and  silica  as  determined  by  Bischof  can  be  represented 
graphically  as  in  Fig.  22. 


-3 1 8 id 22 13 16 IF 

MOLECULES  OF  Si02   TO  ONE  MOLECULE  OF  Al203 
Fig.  22.  Seger's  Si02— A1203  curve. 


1  Seger's  collected  writings,  Vol.  I,  p.   545,  A.  C.  S.  Trans. 


PURDYj 


QUALITIES   OF   CLAYS    FOR    MAKING    PAVING    BRICK. 


213 


Two  important  facts  arc  shown  in  these  curves. 

First.  That  the  kaolin-silica  mixtures  are  more  fusible  than  the  alumin- 
ium and  silicon  oxide  mixture  of  an  equivalent  chemical  composition. 

Second.  That  Kaolin  containing  58.2  per  cent  flint  practically  the  same 
fusibility  as  one  containing  83  per  cent,  while  the  kaolin-silica  mixtures 
containing  percentage  of  silica  between  these  two  limits  are  more  fusible 
than  either. 


J\ 

SEGER  CONES 

i                                   t*                                 li-                                  Kd                                 to                                  Co 
?                                   Vi                                 <£                                   C 

o 
t 

&«3 

^■l 

^° 

APPROXIMATE  DECREES     CENTIGRADE 
Fig.  23.  Melting  points  of  mixtures  of  magnesite  and  Zettlitz  kaolin.    (After  Rieke.) 

Dr.  Eieke2  has  shown  that  magnesite  will  flux  kaolin,  as  is  shown  in. 
Fig.  23.  From  Dr.  Eieke's  results  it  would  seem  that  a  mixture  of 
85  per  cent  kaolin  and  15  per  cent  magnesium  carbonate  has  approx- 
imately the  same  fusion  point  as  43  per  cent  kaolin  and  57  per  cent 
magnesite. 

Dr.  Mellor1  has  shown  a  similar  fusion  phenomenon  with  mixtures 
of  feldspar  and  quartz,  as  exhibited  in  Fig.  24. 

Surprising  as  are  the  facts  shown  in  these  three  curves,  there  has 
been  but  very  little  effort  to  determine  similar  relations  between  the 
several  pairs  of  oxides  and  compounds,  and  practically  none  to  demon- 
strate the  fusion  behavior  of  the  several  oxides  and  compounds  in 
triple  and  quadruple  combinations,  and  yet  this  is  the  very  data  that 
must  be  worked  out  before  much  can  be  accomplished  in  the  interpre- 
tation of  a  chemical  analysis.     When  ceramic  technology  reaches  this 

1  "Brick,"  p.  170,  Oct.  1906. 

2  Trans.  Eng.  Cer.  Soc,  p.  51,  1904-5. 


214 


PAVING   BRICK   AND    PAVING    BRICK   CLAYS. 


[BULL.    NO. 


/ 

/ 

/ 

/ 

/ 

/ 

a 

30         40         50         CO         70 
PERCENT  FLINT 


80        90       100 
Fig.  24.   Mellor's  fusion  curve  for  flint- feldspar  mixtures. 


state  of  progress  an  explanation  can  perhaps  be  made  regarding  the 
fact  that  in  some  cases  the  admixture  of  the  refractory  kaolin  will  canse 
a  lowering  of  the  fusion  point,  while  the  admixture  of  a  flux  such  as 
feldspar  to  the  same  mixture  raises  the  fusion  point.2 

In  the  following  Tables  XXVI  and  XXVII  will  be  found  the  per- 
centages of  the  various  oxides  into  which  the  clays  considered  in  this  re- 
port have  been  resolved.  In  Tables  XXVIII  and  !£XIX  will  be  found 
the  molecular  composition  of  the  clays  as  calculated  from  the  analysis. 
In  Table  XXX  will  be  found  the  results  of  a  rational  analysis  of  clays 
now  used  for  paving  brick  manufacture  in  the  State. 

Xo  attempt  to  interpret  this  data  can  be  made  at  this  time.  After 
a  discussion  of  the  pyro-chemical  properties  of  clays  this  data  will  be  re- 
ferred to  with  the  endeavor  to  show  all  the  possible  relation  there  may  be 
developed  between  the  physical,  chemical  and  pyro-chemical  properties 
of  clays. 


lSee  A.  C.  S.  Trans.,  Vol.  V,  p.  158. 


PURDY]  QUALITIES   OF   CLAYS   FOR    MAKING    PAVING    BRICK.  215 

Table  XXVI. 


SiOg 

Fe203 

A1203 

CaC 

MgO 

Na20 

K.,0 

Moisture. 

Ignition. 

FeO 

Ti02 

S 

K    1  .. 

63.36 

1.80 

15.43 

.93 

1.58 

.56 

3.28 

.48 

6.99 

4.02 

1.00 

27 

K    3  .. 

59.34 

3.26 

15.36 

.76 

1.82 

.80 

3.82 

.29 

7.89 

3.84 

1.31 

.16 

K    4  . 

60.31 

5.04 

17.74 

.41 

1.96 

1.07 

2.88 

.81 

6.71 

1.96 

.84 

.14 

K    5  .. 

63.43 

1.52 

16.89 

1.00 

2.11 

.20 

2.03 

.46 

5.97 

4.24 

1.07 

.11 

K    6  .. 

63.62 

3.02 

16.28 

.63 

1.44 

1.50 

2.60 

.38 

5.88 

2.90 

.96 

.11 

K    7  . 

59.86 

1.42 

17.43 

1.05 

2.32 

.18 

2.80 

.20 

6.35 

5.10 

1.61 

.13 

K  14  . 

64.09 

2.65 

14.16 

1.69 

1.64 

.77 

2.90 

.51 

6.47 

3.16 

.89 

.24 

K  15  .. 

58.03 

2.91 

17.72 

1.42 

1.43 

1.40 

2.66 

.97 

6.47 

5.77 

1.02 

.25 

F    1... 

58.52 

4.99 

15.67 

1.05 

1.45 

1.48 

2.94 

2.02 

7.72 

3.37 

.96 

.32 

Table  XXVII. 


SiO, 


Al2Os 


Loss  on 
Ignition. 


Fe203 


CaO 


MgO    Na2OK20 


Moisture. 


K   2 

63.35 
60.89 
68.50 
58.35 
55.18 
54.37 
57.09 
55.02 
56.29 
58.42 
63.41 
58.57 
55.51 
47.29 
55.37 
56.25 
60.93 
56.56 
39.91 
48.41 
63.42 
60.31 
68.15 
62.70 
58.62 

16.27 

16.40 
16.98 
18.09 
19.22 
23.61 
19.07 
20.35 
20.32 
25.05 
18.61 
20.40 
21.81 
15.51 
21.40 
18.79 
17.93 
12.64 
16.43 
18.31 
16.24 
19.11 
12.89 
16.95 
17.74 

K   8 

K  9 

K10 

Kll 

K12 

K13 

S    1 

S     2 

R    1 

R    2 

R    3 

R    4 

H20... 

H23 

H-II 

H-16 

H-17.. 

H-18 

H-21..   .. 

G-IL.     . 

B-1I 

I-Il 

J-II... 

L-II 

4.75 
8.18 
3.54 
7.02 
10  45 
10.09 
7.97 
9.40 
4.39 
8.08 
4.86 
5.95 
8.00 
13.11 
8.75 
7.01 
5.73 
6.02 
21.20 
12.79 
5.14 
6,70 
5.08 
6.76 
6.66 


7.56 
8.20 
5.77 
6.14 

8.19 


6 

7. 
6 
7 
S 
5 
7 
7. 
4.80 
6.72 
8  02 
8.12 
13.56 
4,80 
6.06 
6.62 
6.14 
7.52 
8.98 
8.48 


1.01 

.55 

.99 

1.20 

.56 

1.58 

.80 

.87 

.48 

.46 

41 

.63 

.56 

7.33 

1.76 

2.39 

1.33 

2.22 

7.57 

5.73 

1.64 

2.73 

1.02 

1.17 

1.26 


1.33 
1.61 
1.71 
2.03 
1.67 
1  61 
1.91 
1.70 
2.01 
1.52 
1.16 
1.37 
1.63 
6.19 

.65 
1.33 

.91 
2.75 
5.08 
3.13 
1.87 
1.73 

.59 
1.47 


3.80* 

4.15 

2.97 

4.58 

2.85 

2.78 

4.69 

3  64 

4.46 

2.30 

3.60 

3.27 

3.56 

3.71 

2.41 

4.61 

5.01 

4.82 

3.71 

5.65 

4.83 

1.44 

2.93 

3.03 

3.92 


.31 
.27 
.50 
.81 

1.02 
.60 
.43 
.83 
.79 

1.29 
.68 

1.06 
.02 

1.31 

3.39 

1.49 
.55 

3.70 
.86 
.79 
.86 

3.05 

1.57 
.98 

2.55 


Table  XXVIII. 


Sample 
iNo. 

1 

Location. 

CaO  MgO 

K20 

Na20    FeO 

Fe203 

A1203 

Si,0 

Ti02 

K    1... 
K    3.... 
K    4.... 
K    5.... 
K    6. 

Alton,   111 

Albion,  111 

Springfield,   111 

■  Rdwardsville,   111 

...    0.110 
...    0.090 
...    0.012 
.  ..     0.108 
..      0.070 

0.261 
U.302 
0.282 
0.319 
0.225 
0.339 
0.295 
0.206 
0.236 

0.231 
0.270 
0  178 
0.130 
0.173 
0.174 
0.222 
0.163 
0.204 

0.059    0.369 
0.086    0.354 
0.099    0.156 
0.020    0.356 
0.152!  0.252 
0.017i  0.414 
0.089,  0.309 
0.130    0.461 
0 . 1 55 |  0.305 

0.074 
0.135 
0.181 
0.057 
0  118 
0.052 
0.119 
0.105 
0.203 

1.00 
1.00 
1.00 
1.00 
1.00 
1.00 
1.00 
1.00 
1.00 

6.98 
6.57 
5.78 
6.38 
6.64 
5.84 
7.69 
5.57 
6.35 

0.083 
0.108 
0.06O 
0.081 
0.075 

K    7.... 
K  14.... 
K15.... 
F     1.... 

Streator  P.  B.  Co 

.Western  Brick  Co 

Barr,  .Streator  111 

.Danville  P.  B.  Co.... 

...    0.109 
...    0.217 
...     0.146 
...    0.122 

0.118 
0.080 
0.073 
0.078 

216 


PAVING     BEICK   AND    PAVING    BEICK   CLAYS. 


[BULL.   NO.    9 


Table  XXIX. 


Sample 
No. 

Location. 

CaO 

MgO 

KNaO 

Fe203 

Al„03 

SiO, 

K  2 

St.  Louis,  Mo 

0.113 
0.056 
0.098 
0.121 
0.053 
0.076 
0.078 
0.043 
0.033 
0.040 
0.056 
0.047 
0.121 
0.232 
0.135 
0.320 
0.839 
0.184 
0.144 
0.122 
0.129 
0.260 
0.861 
0.570 
0.149 

0.208 
0.250 
0.257 
0.286 
0.222 
0.255 
0  213 
0.252 
0.156 
0.159 
0.171 
0.196 
0.174 
0.181 
0.129 
0.556 
0.788 
0.294 
0.117 
0.221 
0.141 
0.231 
1.017 
0.436 
0.074 

0.305 
0.331 
0.229 
0.331 
0.194 
0.216 
0.234 
0.287 
0.120 
0.253 
0.209 
0.213 
0.154 
0.321 
0.365 
0.499 
0.295 
0.390 
0.297 
0.234 
0.289 
0.099 
0.313 
0.404 
0.147 

0.296 
0.319 
0.217 
0.216 
0.272 
0.265 
0.196 
0.248 
0.077 
0.199 
0.231 
0.224 
0.166 
0.272 
0.289 
0.684 
0.186 
0.260 
0.372 
0.378 
0.305 
0.205 
0.197 
0.211 
0.200 

1.00 

1.00 
1.00 
1.00 
1.00 
1.00 
1.00 
1.00 
1.00 
1.00 
1.00 
1.00 
1.00 
1.00 
1.00 
1.00 
1.00 
1.00 
1.00 
1.00 
1.00 
1.C0 
1.00 
1.00 
1.00 

6  62 

K  8 

K  9 

Veedersburg,  Ind 

Crawfordsville,  Ind 

6.31 
6  86 

K  10  .... 

Terre  H aute,  Ind 

5  48 

K  11  .... 

Brazil,  Ind 

4  88 

K  13  .... 

Clinton,  Ind 

5  09 

SI 

Moberly,   Mo 

4  60 

S2 

Kansas  City,  Mo 

4  71 

Rl 

Nelsonville,  O 

3  96 

R2 

Portsmouth,  O 

5  79 

R3 

Canton,  O.  (Imp.) 

4  88 

R4 

Canton,  O.  (Metro) 

4  33 

K  12  .... 

Brazil  Fire  Clay 

3  91 

H-ll 

Topeka,  Kan 

5  09 

H  16 

Peoria,  111 

5  78 

H  17.... 

La  Salle,  111 

7  96 

H  18.... 

Sterling,  111 

4  13 

G-II  . 

Coffeyville,  Kan...               

6  64 

I  - 1 1 . 

8  99 

J- II.     . 

Pittsburg,  Kan .. 

6  29 

L-II.     . 

5  62 

B-1I. 

5  49 

H  20.... 

Savanna,  111 

5  18 

H  21.... 

Galena,  111 

4  50 

H  23.     . 

Carbon  Cliff  Shale 

4  39 

Table  XXX. 
Rational  Analysis. 


Sample 
No. 

Clay 
Substance. 

Quartz. 

Feldspar. 

Phos. 

Carbon. 

Soluble 
Salts. 

K  1 

35.90 
48.00 
43.32 
38.92 
41.02 
33.14 
25.28 
53.36 
51.12 

46.60 
26.74 
43.66 
46.54 
39.98 
49.36 
48.54 
22.82 
29.38 

17.50 
25.26 
13.02 
14.54 
19.00 
17.50 
16  18 
23.82 
19.50 

.093 
.078 
.024 
.090 
.067 
.079 
.069 
.125 
.077 

1.44 
1.50 

.72 
1.26 

.63 

.71 
1.01 

.90 

.92     . 

.13 

K  3 

.14 

K  4 

.04 

K  5... 

.08 

K  6 

.38 

K  7  

Trace 

K  14 

.04 

K  15 

.27 

K  1... 

.14 

PURDY]  QUALITIES   OF   CLAYS   FOR    MAKING    PAVING   BRICK.  217 


PRO-PHYSICAL    AND    CHEMICAL    PROPERTIES    OF    PAV- 
ING BRICK  CLAYS. 

[By   Ross   C.   Purdy.] 
INTRODUCTION. 

Relations — In  the  discussion  of  the  physical  properties  of  clays  it  was 
shown  that  there  is  a  possibility  of  making  some  correlations  between 
the  several  physical  factors.  It  was  also  demonstrated  that  the  physical 
jjroperties  affect  the  adaptation  of  clays  to  processes  of  manufacture. 
No  relation  was  found  to  exist  between  the  chemical  composition  and 
working  properties,  so  no  attempt  was  made  to  correlate  the  chemical 
and  physical  properties. 

We  are  now  to  consider  those  properties  of  clays  which  are  manifested 
in  the  process  of  burning,  and  it  is  here  that  we  should  be  able  to  trace 
the  combined  effect  of  the  physical  and  chemical  properties.  In  burn- 
ing, the  physical  and  chemical  properties  of  raw  clays  surely  operate  as 
causes  having  as  effects  the  pyro-physical  and  pyro-chemical  proper- 
ties. If,  knowing  the  physical  and  chemical  composition  of  the  raw 
clays  and  the  pyro-physical  and  chemical  effects  produced  in  burning, 
we  are  not  able  to  trace  a  logical  and  invariable  sequence  between  the 
causes  and  effects,  we  will  be  forced  to  admit:  either  (a)  That  accord- 
ing to  the  data  at  hand,  clays  having  similar  physical  and  chemical 
properties  in  the  raw  state,  may  behave  differently  in  burning,  or,  (b) 
That  it  is  at  present  impossible  to  determine  exactly  the  physical  and 
chemical  condition  of  raw  clays;  or,  (c)  It  is  impossible  to  trace  the 
effect  of  individual  physical  and  chemical  properties  where  so  large  a 
number  of  changes  occur  simultaneously;  or,  (d)  That,  reasoning  from- 
analytically  determined  causes  to  observed  effects  is  an  absurdity  if  the 
evidence  does  not  permit  of  a  reverse  reasoning,  i.  e.,  from  effect  to 
cause. 

The  first  case,  that  of  clays  of  similar  character  behaving  differently 
in  burning,  is  forcibly  illustrated  in  the  case  of  fire  clays.  Fire  clays, 
having  similar  ultimate  chemical  composition  and  size  of  grain,  may 
have  radically  different  pyro-physical  behavior.  The  one  may  burn  to 
-an  open  porous  mass  at  cone  11,  being  fit  for  fire  brick  purposes;  the 


218  PAVING    BRICK   AND    PAVING    BRICK   CLAYH.  [bull,  no    6 

other  may  burn  quite  dense  at  cone  8,  being  fit  for  stoneware,  sewer  pipe, 
etc.  This  fact  was  noted  in  the  preliminary  report  on  fire  clays,1  and 
will  be  illustrated  in  this  report  under  the  topic  "Changes  That  Take 
Place  During  Fusion." 

The  second  case,  the  impossibility  of  determining  exactly  the  physical 
and  chemical  condition  of  raw  clays,  is  illustrated  bv  the  fact  that  in 
the  more  exact  of  the  two  analyses,  the  chemical,  chemists  do  not  claim 
to  be  able  with  ordinary  care  and  attention  to  details,  to  determine  all 
of  the  elements  that  may  be  in  a  clay,  nor  do  they  claim  to  be  able  In 
determine  the  combinations  in  which  these  elements  exist. 

'Hie  third  case,  or  the  impossibility  of  tracing  the  effect  of  several 
changes  in  physical  and  chemical  conditions  which  take  place  simultan- 
eously, is  a  well  recognized  fact.  On  a  rectangular  coordinate  diagram, 
two  changes;  on  a  triangular  coordinate  diagram,  three  changes  in 
properties  can  be  traced  with  accuracy.  No  simple2  method  has  yet 
been  devised  by  which  the  effect  of  changes  in  four  factors  can  be 
traced,  and  it  is  certainly  beyond  the  capacity  of  the  human  mind  to 
follow  the  effects  of  four  or  more  changes,  if  they  cannot  be  plotted 
diagrammatically.  In  the  case  of  several  clays,  no  two  of  which  agree 
exactly  in  their  several  properties,  and  in  all  of  which  there  are  a  great 
many  properties  peculiar  to  the  individual  clays,  it  is  manifestly  beyond 
our  ability  to  satisfactorily  folloy  even  all  the  known  details.  Broad 
generalizations  with  numerous  and  well-known  exceptions  are  the  best 
that  experimenters  have  been  able  to  make  from  synthetical  mixtures 
of  fairly  pure  clays.  It  is  obvious,  therefore,  that  with  a  heterogeneous, 
assortment  of  impure  clays,  conclusions  concerning  the  relation  between 
the  causes  (the  physical  and  chemical  properties  of  raw  clay)  and  ef- 
fects (the  pyro-physical  and  chemical  properties)  cannot  be  other  than 
broad  generalizations. 

The  last  case,  that  of  the  absurdity  of  claiming  validity  for  deduc- 
tions drawn  by  reasoning  from  cause  to  effect  in  cases  where  data  do  not 
permit  of  a  reverse  reasoning,  i.  e.,  from  effect  to  cause,  is  verv  nicely 
illustrated  in  the  work'  of  Hoffman  and  Desmond3  where  an  attempt 
was  nride  to  devise  an  indirect  method  of  determining  the  refractori- 
ness of  clays.  With  a  given  furnace  operating  on  a  predetermined  time- 
temper^ture  schedule,  they  thought  they  were  successful  in  determining 
the  relative  refractoriness  of  clays  by  toning  up  low  grade  clays  with 
the  addition  of  refractory  material,  and  toning  down  high  grade  clays 
by  the  addition  of  known  amounts  fluxes,  until  the  clays  had  the  same 
refractoriness   under   the   same   heat   treatment.      This    scheme   worked 

1  State  Geol.  Surv.  of  111..  Year  Book  1906.  p.  138. 

2  Solid  figures  are  used  by  physical  chemists  in  depicting-  the  combined  effect 
of  more  than  three  factors,  but  the  drawing-  of  such  figures  to  scale  according  to 
given  data  presents  difficulties  which  the  -writer,  at  least,  has  been  unable  to  sur- 
mount. Judging  from  the  fact  that  ceramists  and  other  technical  scientists  have 
not  as  yet  used  solid  figures  it  must  be  inferred  that  others  have  also  found  the 
involved  difficulties  insurmountable. 

3  Trans.  Am.  Inst.  Min.  Eng.,  Vol.  XXIV,   p.  32. 


PURDY]  QUALITIES   OF   CLAYS    FOR    MAKING    PAVING   BRICK.  219 

nicely  until  they  assumed  definite  temperatures  and  attempted  to  pre- 
pare mixtures  that  would  fuse  at  these  temperatures.  In  the  first  in- 
stance they  adopted  a  certain  combination  of  "causes"  and  measured 
the  "effects."  Tn  the  second  instance  they  adopted  an  "effect"  and  at- 
tempted to  determine  the  combined  "causes"  that  produced  this  effect. 
In  this  they  failed  so  utterly  that  they  abandoned  this  indirect  method 
of  estimating  refractoriness.  If  their  careful  researches  demonstrated 
no  other  fact  than  the  futility  of  attempting  to  draw  conclusions  con- 
eerning  the  relation  between  cause  and  effects,  when  the  data  show  thi= 
relation  operating  only  in  one  direction,  i.  e.,  only  from  cause  to  effect 
or  from  effect  to  cause,  their  work  was  worth  while  and  their  report  a 
valuable  addition  to  ceramic  knowledge. 

Relative  Importance  of  Raw  and  "Burning"  Properties — It  is  plain 
that  the  physical  properties  of  a  raw  clay  influence  its  behavior  mainly 
in  the  machines  and  dryers.  True,  the  physical  properties  have  their 
influence  on  the  burning  behavior  of  clays,  and,  as  in  case  of  size  of 
grain,  if  the  causes  of  the  physical  properties  were  determinable,  their 
findings  would  be  of  value  in  predicting  and  explaining  the  properties 
developed  in  burning.  Size  of  grain,  as  will  be  shown,  is  an  important 
factor  in  the  case  of  pure  minerals,  but  when  the  grains  do  not  have  a 
homogeneous  mineral  composition,  but  are,  in  the  main,  clots  of  minute 
particles  of  several  minerals,  or  particles  of  the  same  mineral  substance 
cemented  together,  any  data  concerning  the  influence  of  fineness  of 
grain  on  the  properties  developed  in  burning  are  apt  to  be  very  mis- 
leading.    Grout's  analysis  of  the  grains  of  clays,  given  on  pages 

shows  that  the  grains  are  not  individual  particles  but  are  aggregates, 

and  Fox's  results,  cited  on  pages confirm  the  conclusions  drawn 

from  Grout's  data.  The  writer  has  ground  impure  clays  until  they 
passed  sieves  of  different  meshes  ranging  from  10  to  200,  molded  the 
clays  into  cones  and  noted  the  effect  of  fine  grinding  on  the  refractori- 
ness of  the  resulting  masses.  The  difference  between  the  ultimate 
fusion  failure  to  stand  erect  under  high  heat  treatment  of  the  cones 
prepared  from  the  same  clay  but  differing  in  size  ,of  grain,  was  hardly 
observable.  True  there  was  a  difference  in  that  the  finely-ground  sam- 
ples vitrified  earlier  and  did  not  lag  as  much  in  bending  over  so  that 
they  could  be  said  to  be  a  trifle  less  refractory.  In  no  case,  however, 
was  the  difference  in  refractoriness  between  the  10  and  200  mesh  sample 
of  the  same  clay  more  than  20  to  40  degrees  centigrade,  as  measured  by 
LeChatelier  electric  resistance  pyrometer. 

[ndirectly,  fineness  of  grain  affects  the  burned  product  in  that  in- 
irriial  fractures  produced  in  drying  and  lamination  in  the  machine 
dies  caused  by  extreme  fineness  of  grain  weaken  the  finished  product. 
These  and  similar  considerations  are  not  properly  considered  under  the 
topic   of   Pyro-physical    and    Chemical   Products. 

The  main  consideration,  in  an  analysis  of  the  influence  of  the  sev- 
eral properties  of  clays,  is  their  influence  on  the  character  of  the  pro- 
duct manufactured  from   the  clays  in  question.     In  the  case  of  paving 


220  PAVING   BRICK   AND    PAVING   BRICK   CLAYS.  [bull.  no.  9 

brick  the  desired  character  of  product  is  toughness  or  resistance  to  im- 
pact and  abrasion.  If  coarse  as  well  as  fine  grained  clays,  plastic  as 
well  as  non-plastic  clays,  and  tough  clays  or  clays  that  show  but  little 
tensile  strength,  can  be  burned  so  as  to  make  tough  bricks,  it  is  obvious 
that  it  will  be  impossible  from  such  physical  data  to  predict  the  char- 
acter of  ware  which  a  given  clay  will  make.  Inability  to  trace  the  in- 
fluence of  so  many  factors  may  be  largely  responsible  for  this  seeming 
lack  of  relation  between  the  physical  properties  of  the  raw  clay  and 
the  properties  of  the  burned  ware,  but  the  fact  remains  that  such  is 
the  case. 

On  the  other  hand  it  can  be  shown  that  there  is  a  possible  or  seem- 
ing relation  between  pyro-physical  and  chemical  properties  and  the 
properties  of  the  burned  ware.  Such  a  relation  has  been  shown  to 
exist  in  the  case  of  fire  clays.  In  the  case  of  paving  brick  clays  there 
is  not  quite  so  distinct  a  relation  between  these  factors,  but  still  it  is 
observable.  The  study  of  the  pyro-physical  and  chemical  changes  pro- 
duced in  clays  by  heat  is,  therefore,  of  considerable  more  importance  in 
the  study  of  paving  brick  clays  than  the  study  of  the  physical  prop- 
erties of  the  raw  clay. 

DEHYDRATION. 

Nature  of  process — Pure  kaolin,  the  basic  clay  substance,  contains  in 
round  numbers  14  per  cent  of  water,  chemically  combined.  At  ordin- 
ary drying  heats  the  amount  of  this  chemically  combined  water  in  the 
kaolin  is  supposed  to  be  unaltered.  In  fact,  there  is  experimental  evi- 
dence to  support  the  belief  that  there  is  some  water  mechanically  re- 
tained by  the  clay  even  at  the  highest  heat  ordinarily  attained  in  any 
dryer,  but  this  has  no  relation  to  the  chemically  combined  water. 

Since,  however,  in  the  ordinary  clay  or  shale  but  a  fractional  part 
of  the  whole  is  kaolin,  ranging  from  a  possible  100-  per  cent  in  the 
purest  varieties  down  to  25  per  cent  or  less  in  the  more  impure  clays, 
it  is  not  surprising  that  the  amount  of  chemically  combined  water 
varies  greatly  in  the  different  clays.  Even  in  the  purest  it  varies 
to  some  extent,  amounting  in  some  cases  to  more  than  14  per  cent.  In 
these  not  rare  cases  some  other  hydrous  minerals  are  supposed  to  be 
present  that  carry  a  higher  percentage  of  combined  water.  It  is  aside 
from  our  purpose  to  dwell  upon  the  kind  and  nature  of  the  hydrous 
minerals  that  may  occur  in  clay  except  to  note  that,  if  they  occur  in 
the  purest  types  of  clays,  and  especially  those  which  have  not  been  moved 
from  their  place  of  formation,  it  is  reasonable  to  suppose  that  in  a 
heterogeneous  mixture  of  minerals  such  as  shales  seem  to  be,  these 
highly  hydrous  minerals  may  in  some  cases  be  present  in  considerable 
quantities.  Since  each  hydrous  mineral  substance  retains  its  chemically 
combined  water  with  a  tenacity  peculiar  to  itself,  it  follows  that  the 
period  of  dehydration  of  clays  will  vary  with  each  variation  in  quan- 
tity and  kind  of  hydrous  minerals  present.  Likewise  the  physical 
alteration  in  the  mass  at  this  period  will  vary  with  each  variation  in 


purdyJ  QUALITIES   OF   CLAYS   FOR    MAKING    PAVING   BRICK.  221 

kind  and  quantity  of  hydrous  minerals  present.  Since,  however,  it  is 
impossible  to  gather  reliable  data  as  to  the  mineralogical  constitution 
of  the  impure  clays,  the  quantities  of  these  hydrous  minerals  present 
must  be  me  re  speculation.  Jhe  varying  effects  produced  during  the 
period  of  dehydration,  which  probably  originate  in  variable  mineralog- 
ical composition,  are  the  only  known  or  determined  facts  in  the  case. 

From  the  foregoing  considerations  it  is  not  surprising  that  the  tem- 
perature of  dehydration  has  been  considered  as  ranging  from  550  to 
650°  centigrade  (990  to  1170°  Fahrenheit),  and  that  there  are  clays 
which  can  withstand  a  heat  treatment  of  16  hours  duration  at  a  tem- 
perature which  will  average  during  this  period  at  least  650°  C.  without 
entire  loss  of  plasticity. 

Six  clays  (K  5,  H  16,  K  8,  K  13,  K  14,  K  15)  after  subjection  to 
a  heat  treatment  supposedly  sufficient  to  affect  complete  dehydration, 
slaked  down  in  water  to  a  red  plastic  mass  similar  to  that  produced  from 
hard  shale  on  weathering.  If  it  is  true  that  on  dehydration  clay  loses 
the  properties  that  cause  the  mass  to  exhibit  plasticity  then  these  clays 
were  not  dehydrated.  If  clays  that  have  been  subjected  to  just  sufficient 
heat  treatment  to  cause  their  complete  dehydration  still  retain  consid- 
erable plasticity,  then  many  will  have  to  change  their  conception  as  to 
the  cause  of  plasticity,  for  surely  nearly,  if  not  all,  of  the  physical 
properties  of  the  kaolin  particles  must  be  altered  by  dehydration.  These 
six  clays  tested  continued  to  lose  weight  after  this  period.  This  loss 
may  possibly  be  accounted  for  by  the  loss  of  volatile  matter  other  than 
chemically  combined  water.  In  the  absence  of  analytical  data,  however, 
it  was  fair  to  assume  that  this  additional  loss  was  in  part  at  least  due  to 
the  further  expulsion  of  the  chemically  combined  water.  If  this  as- 
sumption is  correct,  these  cases  would  indicate  that  the  usually  allotted 
range  in  temperature  for  this  period  is  altogether  too  limited.  If  a 
clay  can  withstand  heat  treatment  for  16  hours  at  a  temperature  that 
ranges  from  500°  to  740°  C,  with  an  average  equal  to  650,  without 
complete  loss  of  its  combined  water,  it  is  fair  to  conclude  that  the  max- 
imum temperature  limit  for  the  dehydration  period  is  above  700°   C. 

Loss  due  to  Constituents  other  than  Combined  Water — The  actual  loss 
in  weight  of  a  clay,  aside  from  loss  of  the  chemical  water,  up  to  this 
temperature  may  in  part,  according  to  Prof.  Orton1  be  accounted  for 
as  follows: 

Vegetable  tissues,  such  as  roots,  leaves,  etc.,  ignite  and  burn  at  about 
300°C. 

Bituminous  matter,  common  to  shales,  ignites  and  burns  between  300 
and  400°C. 

Graphitic  carbon,  does  not  ignite  much  before  500°C. 

Sulphur  distils  from  iron  pyrites  between  400  and  600°C. 

Calcium  carbonate  decarbonizes  between  600  and  1000°C. 

Ferrous  carbonate   decarbonizes  between   350  and  430°C. 


lAmer.  C.  Soc,  Vol.  V,  p. 


222  PAVING   BRICK   AND    PAVING    BRICK   CLAYS.  [bull.  no.  9 

The  loss  of  any  or  all  these  constituents  would  not  materially  affect 
the  plasticity  of  clay,  and  in  the  main  these  reactions  would  be  com- 
pleted before  or  at  the  same  time  as  dehydration.  In  caes  of  K  14  be- 
fore referred  to,  they  had  all  evidently  been  completed  before  the  com- 
pletion of  dehydration,  except  perhaps  the  decarbonation  of  the  small 
amount  of  contained  calcium  carbonate.  The  bricks  were  thoroughly 
oxidized  and  normal  salmon-colored  throughout.  In  this  case  the  only 
possible  conclusion  seems  to  be  that  dehydration  of  clay  requires  more 
heat  than  heretofore  supposed. 

It  has  been  demonstrated  by  Hopewood1  that,  aside  from  the  loss  of 
combined  water,  solid  carbon,  carbonic  acid  gas,  sulphur,  etc.,  quite 
a  large  variety  of  acids  and  bases2  are  expelled  from  the  clay  by  vola- 
tilization at  temperatures  below  the  maximum  required  for  complete 
dehydration.  The  evidence  given  to  Hopewood's  experiments,  together 
with  the  vast  accumulation  of  data  by  agricultural  chemists,  makes  it 
appear  as  though  the  absorbed  as  well  as  the  a&sorbed  salts  are  seriously 
affected  during  this  period.  Direct  evidence  is  not  at  hand  that  would 
throw  light  on  this  question,  but  the  value  of  such  evidence  is  con- 
sidered by  the  writer  to  be  of  such  importance  that  an  extensive  re- 
search dealing  with  this  subject  has  been  outlined.  It  is  anticipated 
that  the  manner  in  which  this  period  of  burning  (dehydration)  is 
conducted  will  be  found  to  play  a  very  significant  role  in  the  character 
of  the  ware  developed  in  "the  finishing  heats."     * 

OXIDATION. 

General  Conditions. 

Definition  of  terms — "Oxidation"  and  "Reduction"  are  chemical 
terms  referring  respectively  to  taking  on  and  giving  off  of  oxygen. 
When  a  piece  of  iron  is  rusting  it  is  becoming  oxidized,  i.  e.,  the  metal 
(Fe)  is  being  converted  to  an  oxide  of  iron  (Fe203)  which  is  red  in 
color.  Iron  rust  can  be  reconverted  to  the  unoxidized  metallic  state 
again  by  application  of  heat  under  reducing  conditions,  i.  e.,  condi- 
tions that  favor  separation  of  the  metallic  iron  and  oxygen.  When  the 
quantity  of  oxygen  in  combination  is  reduced,  then  it  is  said  that  re- 
duction has  taken  place.  When  the-  quantity  of  oxygen  in  combination 
has  been  increased  then  it  is  said  that  oxidation  has  taken  place. 

Evidence  of  reduced  condition  in  raw  clay — "Blue"  clay  and  dark 
gray  shale  owe  their  characteristic  blue  color,  in  the  main,  to  two 
classes  of  substances,  (1)  the  ferrous  compounds,  principally  ferrous  car- 
bonate and  (2)  carbon.  Partially  metamorphosed  carbon  adds  to  a  clay 
mass  its  characteristic  black,  just  as  does  lamp  black  when  added  to 
what  would  otherwise  be  a  white  mass.  Lamp  black,  an  amorphous 
form  of  carbon,  is  the  product  of  decomposition  of  carbon  compounds 

1  Trans.   Eng.   Cer.   Soc,   1904-5.   p.    37. 

2  R.  K.  Meade  has  shown  analytical  data  in  support  of  his  claims  that  the 
alkalies  in  cement  mixtures  are  expelled  during  the  burning-.  "Portland  Cement" 
p.  124. 

J.  W-  Mellor  also  shows  with  data  that  the  loss  of  alkalies  from  fire  clays  fired 
at  1400°C.,  amounts  to  20  per  cent  of  the  total  alkalies  present  in  the  unburned 
clay.     Trans.  Eng.  Cer.  Soc.  Vol.  VI,  p.  130. 


PURDY]  QUALITIES   OF   CLAYS    FOR    MAKING    PAVING    BRICK.  22H 

under  the  influence  of  heat,  resulting  from  conditions  that  prevent  its 
complete  oxidation.  The  carbon  in  shales,  at  one  time  a  part  of  the 
fibrous  tissue  of  living  plants,  was  buried  in  deposits  of  sea  mud,  and  is 
found  today  in  this  same  mud  hardened  into  shale.  Therefore,  the  dark 
iron  compounds  and  the  metamorphosed  remains  of  carbon  compounds 
combine  to  give  the  characteristic  blue  color  to  shales  and  many  fire 
clays. 

Evidence  of  oxidation  in  raw  clay — Where  the  shale  is  covered  with 
only  a  very  thin  "stripping,"  the  color  of  the  upper  three  or  four  feet 
of  the  bank  will  be  red.  In  the  lower  portion  of  these  red  strata  the 
color  shades  off  gradually  into  the  blue  of  the  more  solid  strata  below. 
In  this  red  portion  near  the  top  of  the  bank  the  ferrous  compounds 
have  been  oxidized  to  ferric  compounds  by  the  action  of  the  oxygen 
from  the  atmosphere.  Below  the  belt  of  weathering,  the  clay  retains 
its  blue  color  owing  to  the  fact  that  either  air  cannot  penetrate  to  those 
depths  or  that  its  oxygen  is  largely  spent  before  it  can  reach  the  lower 
limit  of  the  belt  of  weathering.  It  is  observed  that  oxidation  starts 
at  the  surface  and  proceeds  downward.  The  depth  to  which  evidence 
of  oxidation  can  be  seen  depends  upon  the  nature  and  amount  of  the 
oxidizable  mineral  present,  the  solidity  of  the  rock  mass,  the  prevailing 
atmospheric  conditions  and"  the  length  of  time  of  exposure. 

Oxidation  of  Clay  in  Burning. 

The  very  same  processes  that  are  effective  in  oxidizing  the  blue  shale 
to  "red  outcrop"  are  operative  in  burning  when  the  blue  clay  brick  is 
converted  into  "salmon  brick."  In  nature,  at  ordinary  temperatures 
and  under  varying  conditions,  this  oxidizing  process  is  very  slow,  but 
in  the  kiln  at  temperatures  ranging  from  500  to  800°  centigrade,  with 
the  high  draft  that  is  usually  maintained  at  this  early  stage  of  the 
burning,  conditions  under  which  oxidizing  processes  operate  are  very 
much  intensified  and  consequently  comparatively  rapid  in  their  action. 
In  the  case  of  surface  clay,  and  red  clays  generally,  oxidation  is  so 
rapid  that  the  lag  in  time  incident  to  raising  heat  in  a  large  kiln  of 
relatively  cold  ware  is  sufficient  to  complete  the  oxidizing  processes. 

In  the  case  of  many  of  the  shales,  the  time  required  to  completely 
oxidize  the  clay  is  so  much  longer  that  either  the  burner  must  "hold 
the  kiln  at  red  heat"  for  a  time,  or,  especially  in  the  case  of  bricks 
which  have  been  set  wet,  evidence  of  incomplete  oxidation  will  be  very 
evident  when  the  bricks  are  drawn.  The  change  in  color  from  blue  in 
the  "green"  ware,  to  red  in  the  salmon  is  the  result  of  oxidation.  Eed 
surface  and  black  centers  are  results  of  incomplete  oxidation.  These 
changes  in  color  are  the  same  indicators  of  oxidation  and  lack  of  oxida- 
tion noted  in  the  case  of  shale  in  the  bank. 

SUBSTANCES    IN    CLAY"   THAT   ARE   AFFECTED   BY   OXIDATION. 

In  general  terms,  the  oxidizable  substances  in  clays  are  carbon  com- 
pounds, carbonates,  nitrates,  sulphites,  etc.  The  most  noteworthy  ox- 
idizable substances  in  clays  are:  Carbon  and  the  carbon  compounds, 
ferrous  carbonate  and  ferrous  sulphide. 


224  PAVING   BRICK   AND    PAVING   BEICK   CLAYS.  [bull.  no.  9 

Carbon  and  the  Carbon  Compounds — Carbon  is  present  in  practically 
all  of  the  secondary  clays  in  forms  ranging  from  unaltered  vegetable 
matter,  humus  and  its  compounds,  to  the  highly  metamorphic  carbon- 
graphite  in  graphitic  shales.  The  least  altered  carbon  ignites  and  ox- 
idizes most  easily  and  the  highly  metamorphosed  carbon  most  difficulty. 
To  the  decomposing  carbon  compounds  and  their  by-products,  the  or- 
ganic acids,  are  due  many  of  the  physical  properties  of  clays.  It  has 
been  shown  in  earlier  pages  that  organic  acids  are  the  main  agents  that 
cause  denocculation,  a  condition  that  must  exist  before  plasticity  can  be 
developed.  It  could  be  readily  shown  that  humic  acid  (C20H2O9)  with 
its  peculiar  properties  of  absorbing  and  holding  heat,  moisture  and 
soluble  salts,  is  a  very  active  agent  in  promoting  chemical  changes  in 
the  mineral  ingredients  of  clay,  thus  altering  the  physical  condition 
of  the  mass.  Unaltered  carbon  compounds  and  their  by-products  are, 
therefore,  not  only  easily  oxidized  in  burning,  but  have  been  highly  ben- 
eficial in  that  they  have  promoted  the  development  of  those  physical 
properties  which,  if  the  carbon  is  not  in  excess,  permit  of  easy  manufac- 
ture into  wares. 

The  more  metamorphosed  the  carbon  compounds  the  less  active  they 
are  in  promoting  physical  and  chemical  alterations  in  the  clay  mass  and 
the  more  difficult  are  they  to  oxidize  in  the  kiln.  For  these  reasons  fire 
clays  and  clay  shales  in  which  the  carbons  compounds  have  been  com- 
pletely converted  to  graphite  are — within  small  areas — more  constant 
in  their  properties,  thus  being  more  constant  in  their  working  and 
burning  behavior,  and  at  the  same  time,  more  difficult  to  burn. 

Ferrous  Carbonate — Ferrous  carbonate  occurs  in  clay  in  various  phy- 
sical conditons  and  sizes  of  grain.  Large  concretions — "nigger  heads" — 
which  are  often  composed  mainly  of  ferrous  carbonates,  are  to  be  seen 
in  most  shale  banks.  Eanging  in  size  from  12  to  18  inches  in  diameter, 
down  to  minute,  almost  microscopic  particles,  these  concretionary  and 
globular  forms  of  ferrous  carbonate  play  a  role  in  burning  clay  wares 
which,  while  most  peculiar,  is  but  little  understood.  The  ferrous  car- 
bonates that  exist  as  finely  precipitated  powder  surrounding  the  other 
mineral  grains  must,  in  burning,  pass  through  the  same  chemical  altera 
ations  as  the  ferrous  carbonate  in  lump  form,  but' under  such  different 
conditions  that  distinction  must  be  made  between  its  behavior  when  in 
these  two  conditions  of  aggregation. 

One  of  these  large  ferrous  carbonate  concretions  pulverized,  pressed 
into  brick  form  and  burned  under  the  same  heat  treatment  required 
to  produce  pavers  from  the  shale  in  which  the  concretion  was  found, 
produced  a  brigh  red  brick  which  possessed  a  toughness  that  was  equal 
to  that  of  the  brick  made  from  shale.  This  experiment  proved  that  the 
clay  mass  which  is  bound  together  by  ferrous  carbonate  in  a  mass  so 
hard  as  to  wreck  ordinary  crushing  machines  like  dry  pans,  and  contain- 
ing a  comparatively  large  quantity  of  ferrous  carbonate,  can  be  burned 
as  safely  and  into  just  as  good  brick  as  the  softer  shale  containing  but 
a  small  quantity  of  ferrous  carbonate  (3  per  cent  of  total  ferrous  iron.) 


purdv]  QUALITIES   OF    CLAYS    FOR    MAKING    PAVING    BRICK.  225 

Iii  this  brick  made  from  the  crushed  concretion  tliere  was  practically 
no  carbon,  while  the  shale  contained  three  quarters  of  one  per  cent- 
While  it  is  true  that  the  carbon  content  of  the  shale  is  so  small  that  no 
difficulty  is  experienced  in  thoroughly  oxidizing  the  mass  under  the  time 
temperature  schedule  required  to  raise  heat  uniformly  in  a  large  kiln, 
vet  it  is  a  significant  fact  that  occasionally  unoxidized  brick  are  drawn 
from  the  kilns,,  and  that  the  mass  containing  a  large  amount  of  ferrous 
carbonate  was  perfectly  oxidized  under  similar  kiln  treatment. 

Singer1  has  shown  that  the  acid  radical  (CO)  is  expelled  from  fer- 
ous  carbonate  at  temperature  below  430  C.  The  basic  radical  (FeO) 
would  thus  be  given  ample  time  to  become  thoroughly  oxidized  to  Fe^O* 
or  Fe^O  before  the  temperature  could  be  raised  sufficiently  to  cause  fusion 
between  the  ferrous  iron  and  the  silicates.  Under  normal  kiln  treatment 
complete  oxidation  of  the  iron  would  be  effected,  provided  the  clay  mass 
contained  but  a  small  amount  of  carbon.  In  the  almost  total  absence 
of  carbon,  our  experiment  with  the  concretionary  mass  proved  that  the 
iron  could  be  quite  readily  oxidized.  As  the  carbon  content  increased, 
the  difficulty  in  oxidizing  a  given  amount  of  ferrous  iron  would  increase-, 
for  between  carbon  and  oxygen  there  is  a  stronger  affinity  than  between 
iron  and  oxygen.  In  case  there  is  a  high  content  of  both  carbon  and 
ferrous  carbonate,  time  would  have  to  be  allowed  in  burning  to  com- 
pletely burn  out  the  carbon  before  the  heat  is  raised.  If  this  should 
not  be  done  the  ferrous  oxide  would  flux  with  the  silicates  causing  an 
early  fushion  in  the  unoxidized  portion  of  the  brick. 

In  case  the  carbon  is  easily  ignited  and  burns  freely  it  has  been  found 
that  the  fires  in  the  furnaces  have  to  be  drawn,  all  air  supply  shut  off 
and  the  carbon  allowed  to  smolder  until  completely  burned  out.  If 
these  precautions  are  not  taken  in  such  cases,  the  heat  from  the  burning 
carbon  will  raise  the  temperature  in  the  kiln  to  the  point  where  the  fer- 
rous iron  will  be  slagged  with  the  silicates.  In  fact,  the  iron  that  was 
originally  in  an  oxidized  condition  would  be  reduced,  and  the  whole  iron 
content  thus  be  brought  to  its  most  active  fluxing  condition. 

Where  the  carbon  is  less  inflammable,  a  longer  time  would  have  to  be 
allowed  for  its  complete  combustion,  but  such  stringent  precautions 
would  not  have  to  be  taken  as  in  the  case  where  the  clay  contained  more 
inflammable  carbon. 

The  chemical  explanation  of  these  cases  is  that  although  the  CO* 
radical  is  expelled  from  ferrous  carbonate  at  an  early  stage  in  burning, 
the  basic  radical  (FeO)  cannot  receive  the  oxygen  required  to  con- 
vert it  to  its  less  active  fluxing  form,  i.  e.,  to  FesOs  as  long  as  there  is 
carbon  left  in  the  clay  mass.  Carbon  having  a  greater  affinity  for  oxy- 
gen than  the  ferrous  iron  will  withhold  it  from  the  iron.  If  a  clay  con- 
tains insufficient  carbon  of  an  easily  inflammable  variety,  or,  if  the  car- 
bon, even  though  present  in  quantity,  is  difficultly  inflammable,  time 
must  be  allowed  to  permit  the  oxygen  to  penetrate  the  brick,  for  oxida- 
tion proceeds  from  the  exterior  towards  the  interior  in  a  manner  similar 
10  the  oxidation  of  shale  in  the  bank  from  the  outcrop  downward. 

l  Class  exercise  under  Orton,  Ohio  State  Univ. 

—15  G 


226  PAVING   BRICK   AND    PAVING   BRICK   CLAYS.  [bull.  no.  9 

High  content  of  ferrous  carbonate  does  not  in  itself  mean  that  trouble 
will  be  experienced  in  oxidation,  nor  does  a  high  content  of  thoroughly 
oxidized  iron  considered  alone  indicate  immunity  from  oxidation 
u-oubles.  The  substance  that  controls  the  manner  in  which  the  oxida- 
iion  period  of  burning  clay  wares  must  be  conducted  is  carbon.  Burn- 
ing carbon  not  only  will  prevent  oxidation  of  the  ferrous  iron,  but  will 
reduce  the  iron  that  may  have  originally  been  in  a  thoroughly  oxidized 
condition.  It  depends,  therefore,  upon  the  amount  and  form  of  carbon 
present  in  a  given  case,  as  to  whether  in  burning  there  must  be  allowed 
a  short  or  long  Oxidizing  period. 

Ferrous  Sulphide — This  very  frequently  occurs  in  clays  as  bright 
yellow  or  white  crystals.  The  first  of  these  forms  is  often  mistaken 
for  gold  because  of  its  similarity  in  color.  It  is  commonly  known  as 
"fool's  gold."  Mineralogically  it  is  known  as  iron  pyrites  or  marcasite, 
depending  upon  its  crystalline  form. 

If  clay  containing  pyrites  is  loosened  and  allowed  to  weather,  the 
pyrites  will  be  desulphurized.  The  iron  will,  in  the  dry,  oxidize  to  the 
hematite  (FesOs),  or,  if  moisture  is  present,  to  limonite  (2  Fe20s- 
"SILO).  The  sulphur  will  at  the  same  time  oxidize  to  sulphurous  or 
sulphuric  acid.  By  weathering,  therefore,  iron  pyrites  can  be  thoroughly 
oxidized  and  the  sulphurous  and  sulphuric  acid  removed  in  solution  by 
percolating  waters.  These  reactions  require  time,  especially  under  dry 
conditions.  Brick  manufacturers  cannot,  under  the  existing  trade  con- 
ditions, weather  their  clay.  The  face  brick  manufacturer,  therefore, 
must  allow  as  little  time  as  possible  to  elapse  from  the  time  that  his 
clay  is  mined  until  it  is  under  fire  in  the  kiln  if  he  wishes  to  avoid  that 
bane  of  the  face  brick  manufacturer,  scumming,  which  results  from  the 
formation  of  soluble  salts  by  the  sulphurous  and  sulphuric  acid  fr  mi 
iron  pyrites. 

To  the  front  brick  manufacturer,  the  presence  of  iron  pyrites  is  not, 
aside  from  the  question  of  scumming,  a  serious  disadvantage,  for  the 
black-slagged  specks  resulting  from  ferrous  iron  from  the  pyrites  fluxing 
with  the  silicates  is  not  objectionable  to  architects.  If,  however,  a  clean 
buff  brick  is  resired  or  if,  for  any  reason,  the  smoother  and  more  uni- 
formly distributed  black  specking  by  the  use  of  pyrolusite  (MnO)  is 
needed,  then  a  clay  practically  free  from  iron  pyrites  must  be  used.  • 

In  face  brick,  soundness  and  color  are  the  prime  requisites.  In  pav- 
ing brick,  toughness  alone  is  the  prime  requisite.  If  a  clay  contains  sul- 
phide of  iron  (pyrites)  scattered  throughout  the  mass,  local  slagged 
spots  scattered  all  through  the  brick  will  be  formed  in  burning.  These 
slagged  spots  will  be  spongy  or  vesicular,  i.  e.,  full  of  cavities,  just  as 
is  the  black  warty  mass  that  appears  on  the  face  of  a  brick  made  from  a 
pyritiferous  clay.  The  local  fused  spots  are  detrimental  to  the  tough- 
ness of  the  i»rick,  not  only  because  they  are  spongy  but  also  because  they 
dre  fused  glassy  ferrous  silicates,  which  are  generally  very  brittle  and 
have  no  property  in  common  with  the  tough,  stony  matrix  which  makes 
up  the  body  of  the  brick. 


PUKDYj  QUALITIES   OF   CLAYS    FOR    MAKING    PAVING    BRICK.  227 

As  in  weathering,  the  first  step  in  the  oxidation  of  iron  pyrites  is  the 
separation  of  the  iron  and  sulphur.  In  the  kiln,  however,,  sufficient 
length  of  time  cannot  be  allowed  to  drive  off  more  than  one  of  the  two 
atoms  of  sulphur.  The  first  atom  is  expelled  early  in  the  oxidation 
period  and  passes  off  in  the  waste  gases  as  sulphurous  and  sulphuric 
acid  gases.  The  remaining  atom  of  sulphur  is  not  expelled  readily,  in 
fact  either  a  very  long  time  or  much  higher  heat  is  required  for  its 
expulsion.  In  the  customary  heat  treatment  in  kilns,  this  last  atom  of 
sulphur  probably  remains  with  the  atom  of  iron  until  a  temperature 
is  reached  that  will  cause  fusion  between  the  iron  and  silicates,  form- 
ing the  black  slag  mentioned  in  preceding  paragraphs.  It  can  be  said, 
therefore,  that  under  the  usual  kiln  treatment,  iron  pyrites  is  oxidized 
as  follows:  (1)  One  atom  of  sulphur  is  oxidized  and  expelled  during 
the  oxidation  period.  (2)  The  other  atom  of  sulphur  is  oxidized  and 
expelled  only  by  long  heat  treatment  ot  higher  temperatures.  (3)  The 
atom  of  iron,  under  the  long  heat  treatment,  will  oxidize  to  the  higher 
oxide  forms  before  slagging  begins,  but  under  the  usual  heat  treatment, 
in  which  sufficient  time  is  not  allowed  for  the  oxidation  and  expulsion 
of  the  last  atom  of  sulphur  at  a  low  temperature  (about  500°C),  the 
iron  is  not  freed  from  its  sulphur  radical  and  oxidized  to  FeO  until  a 
temperature  has  been  attained  that  would  cause  this  FeO  to  flux  with 
silicates. 

From  these  discussions  of  oxidation  it  is  evident  that  a  good  paver 
cannot  be  made  from  a  pyritiferous  clay  unless  it  either  be  thoroughly 
weathered,  or  an  unusually  long  time  be  given  to  thoroughly  oxidize  the 
iron  and  sulphur  before  fusion  is  allowed  to  take  place. 

Other  Substances — There  are  many  substances  other  than  carbon  and 
iron  that  suffer  oxidation,  but  inasmuch  as  their  oxidation  is  not  at- 
tended with  serious  difficulties  and  is,  therefore,  of  little  consequence 
to  the  paving  brick  manufacturer,  they  will  not  be  discussed.  The 
gases  given  off  from  clay  wares  under  oxidizing  and  reducing  conditions 
are  just  now  being  studied  by  ceramists.  By  these  studies  many  phen- 
omena in  fusion,  discoloration,  etc.,  of  pottery  wares  are  being  explained 
and  the  potter  is  receiving  much  benefit.  It  is  not  necessary,  at  this 
time,  to  discuss  the  results  of  these  studies. 

EFFECT   OF   PHYSICAL   AND    CHEMICAL  PROPERTIES    OF    CLAYS. 

The  effect  of  carbon  in  its  different  forms  has  been  discussed.  The 
oxidation  of  ferrous  compounds  in  the  presence  and  absence  of  carbon 
has  also  been  considered.  Certain  other  points  need  be  considered  un- 
der this  heading.  Among  these  are:  distribution  of  the  carbon,  fine- 
ness of  grain  of  the  clay,  iron  in  combination  as  a  stable  or  not  easily 
altered  silicate,  the  structure  of  the  clay  mass,  the  presence  of  moisture, 
and  the  temperature  factor. 

Varied  distribution  of  carbon — If  carbon  is  thoroughly  disseminated 
through  the  mass,  it  will  be  so  surrounded  by  the  mineral  matter  as 
to  cause  slow  oxidation  in  a  manner  similar  to  the  slow  burning  of  a 
fire  banked  with  earth.    If,  on  the  other  hand  the  carbon  is  concentrated 


228  PAVING   BKICK   AND    PAVING   BRICK   CLAYS.  [bull.  no.  9 

in  particles  the  size  of  coal  dust,  oxidation  can  take  place  much  more 
readily.  Anthracite  screenings  added  to  a  clay  either  for  the  purpose 
of  effecting  equal  distribution  of  heat  or  making  the  ware  more  porus, 
seldom  give  trouble  in  oxidation.  The  quantity  of  carbon,  therefore,  is 
not  so  important  a  factor  in  determining  the  oxidizing  behavior  of  clay 
as  its  character  and  distribution.  On  this  account  chemical  analysis 
has  failed  to  give  much  aid  in  detecting  the  difficultly  oxidizable  clays. 

Fineness  of  gram — If  the  clay  itself  is  fine  grained,  and  especially 
if  very  plastic,  it  will  prevent  oxygen  getting  to  the  carbon  and  will 
delay  the  expulsion  of  the  gases  formed  by  the  burning  carbon.  Fur- 
ther, in  case  of  fine-grained  clays,  the  carbon  will  not  be  completely 
oxidized,  i.  e.,  CO  instead  of  CO?  will  be  formed  and  in  escaping  from 
the  center  of  the  bricks  will  keep  the  iron  in  the  outside  portions  in  a 
reduced  condition  long  after  the  carbon  here  has  been  burned  out  and 
time  given  to  oxidize  the  iron  to  the  ferric  condition.  Fineness  of 
grain  of  a  clay,  therefore,  plays  an  important  role  in  the  oxidation  of 
clay  wares. 

Stable  iron  compounds — Iron  combines  with  silicates  in  both  the 
"ous"  and  "ic"  condition,  i.  e.,  we  have  ferrous  silicates  and  ferric 
silicates.  The  instances,  however,  of  iron  in  the  "ic"  condition  com- 
bining with  silicates  are  comparatively  rare.  This  was  shown  in  a  very 
forcible  manner  in  a  series  of  experiments  in  which  the  writer  used 
several  varieties  of  granite  in  porcelain  floor  tile  bodies.  The  granites 
were  obtained  from  different  quarries  in  the  form  of  "spalls"  that  are 
made  when  the  rough  granite  is  cut  into  shapes.  These  spalls  wrere 
ground  to  powder  that  was  as  fine  as  feldspar  and  flint,  as  prepared  by 
millers  for  pottery  use.  In  the  majority  of  cases  the  tiles  were  full  of 
minute  black  specks  with  but  a  trace  of  the  buff  color  that  would  be 
given  if  the  iron  had  been  in  the  "ic"  condition.  In  one  or  two  cases 
the  iron  specks  were  buff  instead  of  black,  showing  that  the  iron  was 
either  in  the  "ic"  form  in  the  granite  or  had  been  oxidized  in  the 
burning.  From  the  fact  that  all  these  "granite  trials"  were  burned 
at  the  same  time  and  hence  under  the  same  heat  treatment,  it  was  con- 
cluded that  in  these  exceptional  cases  the  iron  was  originally  in  the 
more  highly  oxidized  form.  This  conclusion  was  substantiated  in  later 
experiments  in  which  iron  calcines  were  used. 

When  fusion  in  a  clay  or  clay  mixture  has  progressed  sufficiently  tc 
cause  the  whole  to  be  vitrified,  iron,  if  originally  present  as  an  oxide, 
carbonate  or  hydrate,  will  generally -combine  as  a  lower  oxide,  forming- 
ferrous  silicate.  The  blueing  of  fire  clays  and  the  changing  from  red 
to  chocolate  in  shales  is  evidence  of  this.  For  this  reason  iron  oxide 
added  to  a  porcelain  body  either  as  an  oxide  or  as  an  ingredient  of  a 
shale  will,  on  vitrification  of  the  body,  result  in  a  blue  tint.  Iron  pre- 
cipitated into  a  mass  of  silica  or  alumina,  and  the  mixture  dried  and 
calcined  under  oxidizing  conditions,  will  when  added  to  the  porcelain 
body,  produce  a  buff  or  pink,  never  a  blue  color.     These  experiments 


purdyJ  QUALITIES   OF   CLANS    FOB    MAKING    PAVING    BRICK.  229 

proved  conclusively  that  iron  can  combine  with  alumina  and  silica  in 
the  "ic"  condition  forming  ferric  compounds,  and,  further,  that  when 
so  combined  fusion  of  the  body  will  not  result  in  the  reduction  of  the 
iron   compound. 

The  practical  lessons  to  be  learned  from  these  two  experiments,  the 
first  with  granite  dust  and  the  second  with  iron  free  as  an  oxide  and 
combined  as  a  silicate,  are:  (1)  that  when  combined  as  a  ferrous  sili- 
cate the  maintenance  of  strictly  oxidizing  conditions  in  a  kiln  will  not 
result  in  oxidation  of  the  iron;  (2)  that  iron  oxide  uncombined  is  not 
only  easily  reduced  but  will  form  ferrous  compounds  when  fused  with 
silicates;  (3)  that  when  iron  is  combined  as  a  ferric  compound  with 
alumina  and  silica,  it  will  retain  its  ferric  condition  against  the  re- 
ducing influence  of  fusion  and  hence  is  very  apt  to  retain  its  "ic"  form 
even  under  reducing  conditions.  This  latter  statement  is  an  assump- 
tion, for  no  direct  evidence  bearing  on  the  point  is  at  hand,  but  deduc- 
tion from  known  data  seem  to  leave  no  doubt  as  to  the  validity  of  the 
assumption. 

In  clays  we  have  iron  combined  with  silicates  in  a  large  variety 
of  mineral  forms  and  compounds.  If  these  compounds  are  stable  when 
heated,  the  iron  will  retain  its  form  of  combination  against  oxidizing 
and  reducing  influences.  Iron  when  combined  as  a  silicate,  therefore, 
will  not  be  affected  during  the  oxidation  period.  In  this  connection, 
however,  chemical  analysis  of  a  given  clay  will  not  show  exactly  how 
much  of  the  iron  is  combined  or  in  what  form  it  is  combined  with  the 
silicates. 

Structure  of  clay  ware — Orton  and  Griffin  have  shown  that  the  more 
porous  the  brick  the  more  readily  can  it  be  oxidized.  Soft-mud  bricks 
by  actual  porosity  determinations  were  found  to  be  the  most  porous, 
dry-press  somewhat  more  dense,  and  the  stiff-mud  bricks  the  most 
dense.  Our  experiments  have  shown  also,  that  clay  issuing  from  the 
machine  die  in  as  dry  or  "stiff"  a  condition  as  is  compatible  with  form- 
ation of  a  perfect  bar,  will  produce  a  denser  brick  than  when  the  bar  is 
permitted  to  issue  in  a  softer  condition.  While  maximum  density  in 
unburned  bricks  means  minimum  toughness  that  can  be  produced  with  a 
particular  clay,  it  means  also  maximum  difficulty  in  oxidation.  This, 
however,  is  a  minor  factor  in  the  problem  of  oxidation  of  clay  wares, 
for  an  easily  oxidized  clay  will  still  be  easily  oxidized  and  a  difficultly 
oxidized  clay  will  be  difficultly  oxidized,  no  matter  how  dense  the  wares 
may  be  in  either  case. 

The  thickness  of  ware  and  consequently  the  manner  of  setting  is  a 
more  important  factor  than  density  of  the  clay  body.  Hollow  goods, 
where  the  walls  are  thin,  would  be  completely  oxidized  under  conditions 
that  would  not  permit  the  complete  oxidization  of  bricks  manufactured 
from  the  same  clay.  Depth  to  which  oxygen  must  penetrate  is  ob- 
viously the  effective  factor  in  these  cases.    " 


230  PAVING   BRICK   AND    PAVING   BRICK   CLAYS.  [bull.  no.  9 

Temperature  as  a  Factor  in  Oxidation — Quite  obviously,  the  higher 
the  temperature  the  more  rapid  will  be  the  combustion  of  the  carbon. 
In  the  case  of  clays  free  or  practically  free  from  iron,  or  where  the 
iron  is  in  a  stable  silicate  combination,  rapid  combustion  at  high  tem- 
peratures would  have  no  attending  evils  and  would  materially  shorten 
the  oxidation  period.  When  the  iron  is  present  in  the  "ous"  condition, 
or  where  it  can  be  easily  reduced  to  the  "ous"  form,  combustion  of  the 
carbon  at  temperatures  above  1000°  C.  would  result  in  partial  slagging 
of  the  iron  with  the  silicates  forming  a  dark  gray  mass  that  cannot, 
without  expenditure  of  excessive  time,  be  reoxidized.  Such  action  would 
cause  premature  fusion  of  the  clay  mass,  especially  near  the  bag  walls 
of  the  kiln,  and,  as  a  consequence,  careening  of  the  whole  "setting"  or 
at  least  a  falling  over  and  fusing  together  of  the  bricks  near  the  bags. 

Oxidation  at  too  high  temperatures  is  frequently  shown  by  a  per- 
manently discolored  center  or  core,  in  which  vitrification  has  progressed 
further  than  in  the  outside  shell  of  the  brick.  Orton  and  Griffin  found 
that  800°  C  was  the  safest  temperature  at  which  to  oxidize  the  average 
clay.  In  some  rare  cases,  like  the  clay  found  at  Loraine,  Ohio,  which 
Orton  and  Griffin  cited,  even  800°  C  would  be  too  high  for  safe  oxida- 
tion. 

Moisture  as  a  Factor  in  Delaying  Oxidation — In  the  majority  of  yards 
which  were  visited  by  the  writer  evidence  could  be  found  of  incomplete 
oxidation  of  a  few  bricks  in  an  otherwise  thoroughly  oxidized  kiln  of 
brick.  Inquiry  developed  the  fact  that  in  most  instances,  in  the  rush 
to  make  a  day's  work,  the  setters  would  set  the  bricks  as  they  came 
from  the  dryer,  no  matter  how  wet  or  dry  they  may  have  been.  In- 
variably either  the  head  setter  or  superintendent  would  recall  that  a 
carload  or  two  of  wet  bricks  were  set  in  the  particular  place  where  the 
unoxidized  bricks  were  found  on  "drawing  the  kiln."  It  is  evident, 
therefore,  that  moisture  in  the  bricks  has  an  influence  on  oxidation  of 
the  clay. 

Theoretical  calculations,  laboratory  experiments  and  factory  observa- 
tions have  proved  that  wet  brick  set  in  a  kiln  of  dry  bricks,  are  de- 
layed in  heating  up  by  the  fact  that  the  heat,  which  in  case  of  the  dry 
bricks  is  sufficient  to  carry  it  well  into  the  oxidizing  period,  is  spent  in 
evaporating  the  water  from  the  wet  bricks,  thus  delaying  their  Seat- 
ing up"  process.  Bricks  thus  delayed  will  not  be  heated  much  more 
than  is  sufficient  to  cause  the  beginning  of  oxidation,  when  in-  the  bulk 
of  the  bricks  oxidation  is  completed  and  fusion  begun.  Under  these 
conditions  the  bricks  that  were  wet  will  pass  through  the  oxidizing 
period  (450  to  1000°  C)  too  rapidly  to  permit  their  complete  oxidation. 
Water,  therefore,  indirectly  delays   oxidation. 

PHYSICAL    AND    CHEMICAL    EFFECTS    OF    INCOMPLETE    OXIDATION. 

Usual  effects — Seduction  of  iron  and  the  consequent  early  fusion  of 
the  unoxidized  portion  of  a  brick  results  in  the  formation  of  a  par- 
tially fused  glass  surrounded  by  a  shell  that  has  as  a  rule  just  begun  to 
vitrify.     Entrapped  in  this  glass  is  some  burned  carbon  which  when 


PURDY]  QUALITIES    OF    (LAYS    FOR    MAKING    PAVING    BRICK.  231 

partially  oxidized  is  converted  into  a  gas.  Aside  from  the  CO?  formed 
by  the  oxidation  of  the  entrapped  carbon,  there  are  salts  that  are 
volatilized  into  vapors  at  this  heat.  These  gases  and  vapors  expand 
on  heating,  causing  the  black  unoxidized  core  of  the  brick  to  swell  up 
until,  in  extreme  cases,  the  brick  is  twice  its  normal  size  and  will  float 
in  water.  Inasmuch  as  the  oxidized  shell  is  thickest  on  the  edges  and 
thinnest  of  the  faces,  the  swelling  core  wTill  bulge  out  the  faces  of  the 
brick  until  it  approximates  the  shape  of  a  cylinder. 

It  is  obvious  at  once  that  bricks  which  have  swollen  centers  will  not 
be  fit  for  pavers.  It  follows  also  that  the  toughness  of  a  brick  is  lessened 
in  proportion  to  the  extent  that  its  center  is  reduced  and  rendered 
vesicular.  It  is  imperative,  therefore,  that  ample  time  be  given  at 
the  oxidizing  period  (red  heat)  to  insure  complete  combustion  of  the 
carbon  and  oxidation  of  the  iron. 

Exceptional  Effects — In  the  case  of  H,  23,  oxidation  had  not  pro- 
gressed very  far  at  the  end  of  24  hours  exposure  at  650°,  and  the  un- 
oxidized portion  of  the  briquettes  vitrified  on  further  heating  to  as 
hard  hard  and  dense  a  mass  as  did  the  outer  oxidized  portions.  No 
swelling  or  distortion  of  the  brick  due  to  the  oxidation  of  the  carbon 
and  ferrous  iron  was  noted.  In  fact,  the  shrinkage  and  rate  of  de- 
crease in  porosity  was  not  abnormal  in  any  respect.  In  Fig.  25  are 
shown  the  volume-shrinkage,  porosity,  and  specific  gravity  curves  for 
this  clay. 

In  this  figure,  the  specific  gravity,  porosity  and  volume  of  the  bricks 
burned  at  different  temperatures  are  calculated  in  terms  of  the  per- 
centage of  increase  or  decrease  over  those  of  the  unburned  bricks.  In 
other  words,  the  raw  factors  are  considered  as  a  basis  from  which  the 
turned"  factors  are  calculated  as  increase  or  decrease.  Zero,  there- 
fore, represents  the  data  obtained  from  the  unburned  bricks. 

The  percentage  of  increase  of  the  burned  ware  over  that  of  the  un- 
burned is  shown  above  the  datum  line  on  the  ordinate,  and  the  per 
centage  of  decrease  is  shown  below  the  datum  line.  On  the  abscissa 
is  shown  the  actual  percentage  of  porosity  of  the  burned  brick. 

Points  on  the  same  ordinate  represent  a  single  brick.  Data -from  all 
the  bricks  studied  in  this  test  have  not  been  plotted,  but  only  those  in 
which  the  percentage  of  porosity  differed  sufficiently  to  fix  points  on 
the  curves  that  would  show  a  comparative  increase  or  decrease  in  the 
several  factors. 

The  fact  that  the  actual  percentage  of  porosity  of  the  burned  brick 
was  taken  in  each  case  as  a  point  on  the  abscissa,  without  regard  to 
the  porosity  of  the  unburned  brick,  will  account  for  the  irregularity  in 
the  curves. 

Xotwithstanding  the  fact  that  the  black  unoxidized  core  remained, 
even  when  the  whole  exhibited  a  porosity  of  only  2  per  cent,  the  brick 
continued  to  shrink  normally  with  each  increase  of  temperature,  and 
the  specific  gravity  of  the  brick  decreased  less  than  in  the  case  of  many 


232 


PAVING    BRICK    AND    PAVING    BRICK   CLAYS. 


[BULL.   NO.    9 


normally  burned  paving  brick  shales.  This  steady  decrease  in  volume 
and  comparatively  slight  increase  in  specific  gravity  gives  evidence  of  a 
thermo-physical  behavior  that  is  opposite  to  that  of  the  majority  of 
clays  containing  carbon. 


PERCENTAGE    OF 
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Fig.    25.      Physical    alterations   produced    by  burning  compared  with  unburned  con- 
dition   of   clay. 

Fusion1. 

fusion  period  of  clays. 

From  the  laws  of  physical  chemistry,  it  could  not  be  expected  that 
the  heterogeneous  mineral  mass  called  clay,  consisting  largely  of  amor- 
phous materials,  would  have  a  definite  fusion  point.  According  to 
Walker2,  this  would  more  properly  be  called  a  fusion  period. 

1A  large  part  of  this  discussion  of  the  fusion  period  appeared  by  permission  in 
advance  in  a  paper  by  Purdy  and  Moore  in  Trans.  Am.  Cer.  Soc,  Vol.  IX. 
2  Introduction  to  Physical  Chemistry,  p.  6  4. 


purdy]  QUALITIES   OV   CLAYS    FOB    MAKING    PAVING    BRICK.  238 

.Our -studies,  a  part  of  the  data  of  which  are  shown  in  subsequent 
curves,  bear  out  this  statement.  It  will  be  seen  that  in  the  case  of  the 
purest  clays,  according  to  the  specific  gravity  curves,  fusion  begins  as 
early  as  cone  3.  In  the  case  of  some  of  the  most  impure  shales,  high 
in  lime,  fusion  begins  at  a  period  considerably  earlier  than  cone  010. 
Fusion  thus  early  begun  progresses  with  more  or  less  regularity  until 
the  whole  mass  enters  into  active  ther  mo-chemical  reaction1  and  de- 
formation of  the  ware  ensues.  Incipient  vitrification,  vitrification,  and 
like  terms  are  only  descriptive  of  the  effects  at  different  stages  of 
fusion.  It  is  the  rate  of  fusion,  therefore,  that  determines  the  pyro- 
physical  effects  produced  in  the  burning  of  clay  wares  during  this 
period. 

FACTORS   AFFECTING   RATE   OF   FUSION. 

Mineralogical  Composition — Synthetical  studies  of  the  fusion  of  mix- 
tures of  pure  minerals,  have  shown  that  the  same  chemical  elements, 
brought  together  as  constituent  parts  of  different  minerals,  produce 
mixtures  having  unlike  fusion  periods.  The  rate  of  fusion  and  the 
regularity  with  which  it  progresses,  as  well  as  the  point  of  complete 
yielding,  are  affected  very  largely  by  the  manner  in  which  the  various 
elements  are  previously  combined.  Because  of  the  difficulty  of  mak- 
ing a  microscopic  mineralogical  analysis  of  a  clay,  we  are  not  able  to 
obtain  information  that  would  aid  in  an  attempt  to  foretell  or  explain 
in  full  the  fusing  behavior  of  clays.  Eealization,  therefore,  of  the  fact 
that*  difference  in  the  mineralogical  make-up  of  clays  of  like  ultimate 
chemical  constitution,  causes  difference  in  their  fusion  behavior,  is  the 
only  result  of  practical  value  that  has  so  far  come  from  the  study  of 
the  fusion  behavior  of  synthetical  mixtures  of  minerals. 

There  is  one  very  notable  exception  to  the  above,  and  that  is  in  the 
case  of  calcium  carbonate.  The  effect  of  calcium  carbonate,  depending 
upon  size  of  grain  and  extent  and  homogeneity  of  diffusion  throughout 
the  clay  mass,  operates  in  a  two-fold  manner.-  If  thoroughly  blended 
with  the  clay  in  small  particles  a  portion  of  it  (on  the  average  up  to 
about  8  per  cent  of  the  'total  clay  mass)  operates  as  a  very  active  flux. 
Its  fluxing  effect  is  most  notable  on  account  of  the  rapidity  with  which 
it  combines  with  clay  substance  to  form  a  molten  mass.  This  reaction 
is  in  some  instances  so  rapid  as  to  make  it  very  dangerous  to  ap- 
proach the  vitrification  temperature.  If  the  calcium  carbonate  is  pres- 
ent in  nodules,  the  thermo-chemical  reaction  just  described  can  take 
place  only  at  the  points  of  contact  of  the  decarbonized  lime  and  clay, 

l  The  expression  "thermo-ehemical  reaction"  is  used  here  because  we  are  accus- 
tomed to  thinking  of  fusion  as  resulting-  from  chemical  combination  of  the  clay- 
ingredients.  The  idea  conveyed  by  a  literal  definition  of  the  term  is,  however, 
very  erroneous.  The  alterations  in  the  clay  mass  during  fusion  are  more  largely 
that  of  mutual  solution  of  the  mineral  compounds  than  of  chemical  reaction  one 
with  another. 


234  PAVING   BRICK   AND    PAVING   BRICK   CLAYS.  [bull.  no.  9 

the  remainder  of  the  carbonate  being  converted  into  quicklime.  The 
different  effects  of  lime  in  these  two  physical  conditions  one  the  rate 
and  regularity  of  fusion  of  the  clay  mass  is  obvious. 

In  the  very  valuable  researches  recently  published1  by  Dr.  Reinhold 
Rieke,  it  is  demonstrated  that  lime  added  in  excess  of  a  given  amount 
does  not  act  as  a  flux  and  cause  sudden  failure  of  ware  with  slight  in- 
crease of  heat  treatment.  In  fact,  it  happens  that  this  excess  lime  seems 
to  counteract  the  effect  produced  by  the  smaller  quantities.  Experi- 
ments in  the  compounding  of  pottery  bodies  have  shown  that  notwith- 
standing the  fact  that  wares  containing  lime  in  excess  of  this  amount 
clo  not  fail  by  sudden  fusion,  i.  e.,  with  slight  increase  in  intensity  of 
heat  treatment,  they  suffered  a  rapid  decrease  in  porosity,  and  specific 
gravity  when  the  heat  treatment  had  become  sufficiently  intense  to 
cause  the  formation  of  the  more  fusible  lime-silicate  solution.  It  ac- 
cords entirely  with  the  facts  to  conceive  of  the  fused  portion  as  a 
mutual  solution  of  minerals  becoming  saturated  with  lime.  Up  to  the 
point  of  about  one-thircl  saturation  the  lime  is  very  active  as  a  flux  and 
decreases  in  activity  as  the  saturation  approaches  completion.  It  is 
easy  to  see,  therefore,  that  any  lime  which  may  be  present  in  quantities 
in  excess  of  that  which  can  go  into  solution  will  not  have  any  fluxing 
action. 

In  most  mineral  mixtures  (and  this  is  true  in  clays)  the  first  which 
fuses  is  not  the  most  fusible  individual  mineral  or  substance  which  may 
be  present.  The  first  to  fuse  will  be  the  most  fusible  mixture  of  the 
minerals  present  known  technically  as  a  eutectic  mixture.  This  mix- 
ture may  consist  of  two  or  more  of  the  clay  ingredients.  Whatever  the 
mixture  may  be — and  this  depends  largely  upon  the  size  and  character 
of  the  grains — it  will  fuse  some  time  before  the  fusing  point  of  the 
most  fusible  mineral  has  been  reached.  This  is  shown  in  the  curves 
given  in  the  section  of  this  report  which  deals  with  the  chemical  prop- 
erties of  clays. 

Now  (repeating  for  emphasis)  any  lime  in  excess  of  that  which  is 
required  to  form  this  most  easily  fusible  (eutectic)  mixture  which  is 
possible  with  the  kind  and  condition  of  minerals  present  in  a  given 
clay,  will  not  be  active  as  a  flux.  That  portion  of  the  lime  necessary 
to  form  this  eutectic  mixture  goes  into  solution  with  a  rapidity  which 
is  inversely  as  the  degree  of  saturation.  The  lime  which  goes  into 
solution  is  least  active  as  a  flux  when  sufficient  is  present  to-  completely 
saturate  the  fused  portion,  most  active  at  about  one-third  saturation. 

The  rate  of  formation  and  the  amount  of  fused  material  formed  in 
a  brick  very  obviously  determine  the  rate  at  which  the  open  pores  will 
be  eliminated.  Since  lime  readily  forms  solutions  with  silicates,  and 
particularly  with  clay  substance,  those  clays  which  contain  from  2  to  8 
per  cent  of  free  lime  will  vitrify  rapidly.  Other  clays  having  the  same 
ultimate  chemical  composition  as  the  rapidly  vitrifying  ones,  but  in 
which  the  lime  is  already  combined  as  in  a  lime-bearing  silicate,  will  not 
vitrify  rapidly,  other  factors  which  influence  fusion  being  equal.     We 

l  Sprechsaal,  Nos.   45  and  46,  Nov.   1907. 


purdyJ  QUALITIES   OF   CLAYS   FOR    MAKING    PAVING    BBICK.  235 

must  recognize,  therefore,  thai  when  the  other  factors  which  effect  fusion 
are  the  same,  the  amount  of  lime  which  will  combine  to  form  this  most 
easily  fusible  mixture  depends  upon  whether  the  lime  is  free  or  com- 
bined, as  well  as  upon  the  kind  and  relative  quantities  of  the  other 
oxides  present. 

The  per  cent  of  calcium  oxide  which  Eieke  found  would  form  the 
most  fusible  mixture  of  the  formula  XCaO  1  AI2O3  ySiCV  were  as  fol- 
lows : 


XCaO  1  A1,03  1  SiO, 

XCaO  1  AL03  2  SiO, 

XCaO  1  A1,03  3  Si02 

XCaO  1  ALA  4  SiO, 


—  25.6  per  cent  CaO 

—  33.4  per  cent  CaOi 

—  33.1  per  cent  CaO 
— '24.6  per  cent  CaO 


—  7.9  per  cent  CaO 
— 10.0  per  cent  CaOi 

—  9.8  per  cent  CaO 

—  7.5  per  cent  CaO 


In  each  of  these  mixtures  the  per  cent  of  calcium  oxide  taken  into 
solution  up  to  the  point  where  the  rate  of  solution  began  to  decrease 
as  shown  by  his  curves,  were  as  follows : 

XCaO  1  A1A  1  SiO, 

XCaO  1  A1,03  2   SiO, 

XCaO  1  A1,03  3  SiO, 

XCaO  1  ALA  4  SiO, 

Size  of  Grain — The  full  significance  of  this  factor  can  be  appreciated 
only  by  considering  extreme  cases,  as  in  the  case  of  calcium  carbonate, 
above  cited,  or  as  in  a  mixture  of  two  minerals  such  as  feldspar  and 
flint.  When  feldspar  and  flint  are  mixed  as  fine  powders  in  the  pro- 
portion of  75  per  cent  feldspar  and  25  per  cent  flint,  the  mass  will  be 
fused  to  a  fluid  at  approximately  1100  °C  in  a  comparatively  short  time. 
If,  however,  these  two  minerals  were  placed  side  by  side  in  the  shape  of 
rectangular  pieces  having  the  same  proportional  weight  as  in  the  first 
case,  the  only  fluxing  action  that  would  take  place  at  1100  °C  would  be 
at  the  points  of  contact.  Even  if  the  heat  was  held  at  1100  °C,  com- 
plete fusion  of  the  two  pieces  of  mineral  could  only  take  place  when  the 
glass,  formed  at  the  point  of  contact,  enveloped  and  slowly  ate  into  the 
unfused  portions,  and  thus  produced  an  intimate  mixture  of  the  two 
minerals  by  diffusion  or  surface  tension.  It  is  common  experience  that 
if  complete  fusion  of  the  two  minerals  at  1100°C  is  desired  when 
brought  together  in  the  form  of  coarse  particles,  considerable  time  must 
be  allowed,  and  that  to  effect  complete  fusion  in  a  shorter  time,  the 
heat  must  be  raised  from  1100° C  to  1230°C  (approximately),  or  the 
fusing  point  of  feldspar.  At  this  temperature  the  feldspar  melting 
would  completely  envelop  or  perhaps  float  the  flint  particles,  and  slowly 
attack  and  dissolve  them,  just  as  water  will  attack  and  dissolve  a  piece 
of  loaf  sugar. 

The  above  illustration,  while  an  exaggerated  case,  nevertheless  is 
descriptive  of  the  effect  of  fineness  of  grain  on  the  fusion  of  any  two 
minerals  which  the  mutually  soluble,  and  also  descriptive  of  the  fusion 
of  a  mixture  containing  particles  of  several  minerals,  as  a  clay. 

1  This  mixture  is  lime  with  pure  clay  substance.     Note  how  much  more  active 
the  lime   is  in  this  mixture  than  in  the   others. 


236  PAVING   BRICK   AND    PAVING   BRICK   CLAYS.  [bull.  no.  9 

In  the  burning  of  clay  wares,  where  time  is  an  important  and  un- 
avoidable factor,  the  effect  of  fineness  of  grain  influencing  the  fusing 
of  clays  is  particularly  noteworthy.  By  the  manufacturers  of  pyrome- 
tric  cones  it  has  been  recognized  as  such  a  powerful  factor  that  the  ut- 
most care  is  taken  to  maintain  uniformity  in  size  of  grain  in  their 
materials,  both  before  and  after  manufacture  into  "powdered  cone  stock. 

The  statement  has  been  made  in  preceding  paragraphs  that  differ- 
ences in  mineralogical  constitution  cause  differences  in  behavior  of  clays 
during  fusion.  That  statement  is  correct  for  the  heat  treatment  or  time 
and  temperature  required  to  affect  either  the  partial  or  complete  fusion 
of  the  mass.  It  would  not  be  correct,  as  will  be  shown,  if  the  tempera- 
ture alone  was  considered. 

The  mixture  of  minerals  in  a  clay  which  has  been  ground  in  a  dry 
pan  is  far  from  being  homogeneous.  Our  discussion  earlier  in  this 
chapter  of  the  constitution  of  the  grains  should  make  it  plain  that  even 
if  they  were  as  finely  ground  and  as  thoroughly  disintegrated  as  is  prac- 
ticed in  the  potteries,  the  mixture  would  lack  very  much  of  being  homo- 
geneous. Now  the  molten  silicates  are  so  viscous  that  diffusion  in  them 
is  exceedingly  slow  compared  with  diffusion  of  salts  in  water1  and  hence 
a  very  long  time  would  be  required  to  obtain  the  homogeneous  mixture 
that  is  necessary  before  the  mass  will  fuse  at  its  true  melting  point. 

Walker  has  been  quoted  to  the  effect  that  crystalline  substances  have 
a  definite  melting  point  while  amorphous  substances  do  not.  The  reason 
for  this  is  based  very  largely  upon  this  matter  of  absolutely  perfect 
homogeneity  of  constitution.  When  a  substance  crystallizes,  its  com- 
ponents are  as  intimately  and  homogeneously  blended  as  it  is  possible 
to  conceive  of,  hence,  when  the  mass  fuses  the  components  are  in  a 
position  to  dissolve  in  one  another  as  soon  as  a  temperature  is  attained 
at  which  the  solution  is  affected.  In  amorphous  compounds2  we  have 
not  this  intimate  molecular  mixture3  and  hence  not  a  sharp  melting 
point.  In  the  case  of  clays  and  clay  mixtures,  where  we  are  not  able  to 
cause  a  mixture  of  the  components  that  is  any  other  than  a  compara- 
tively very  poor  approximation  to  intimacy  and  homogeneity,  it  must 
be  expected  that  either  an  inordinarily  long  time  will  have  to  be  taken, 
or  a  temperature  higher  than  the  true  melting  point  of  the  mixture 
be  maintained  in  order  to  effect  the  fusion.  This  is  why  in  research 
laboratories  they  either  remelt  the  mixture  at  least  once  before  determ- 
ining its  true  melting  point,  or,  take  it  to  complete  liquid  fusion  and 
note  the  temperature  at  which  the  mass  solidifies.  This  is  also  the 
reason  why  potters  find  that  a  mixture  will  melt  more  easily  the  second 
and  third  time.  This  is  also  one  of  the  reasons  why  so  niuch  stress  was 
laid  by  the  writer  upon  the  mineral  constitution  of  the  grains  as  Grout 
found  them  in  the  West  Virginia  clays. 

1  Diffusion  of  salt  in  water  is  so  slow  as  to  permit  of  easy  measurement.  Diffu- 
sion of  sugar  in  a  cup  of  hot  coffee  is  so  slow  that  it  necessitates  stirring  in  order 
to  dissolve  a  teaspoon  full  of  sugar  within  a  reasonable  time. 

2  Here  reference  is  made  only  to  inorganic  compounds. 

3  This  is  not  the  sole  reason. 


purdy]  QUALITIES    OF    (LAVS    FOR    MAKING    PAVING    BRICK.  237 

Beference  was  made  to  the  attempt  by  Hoffman  and  Desmond  to  tesl 
the  refractoriness  of  clay  by  toning  np  or  down  as  the  case  required. 
The  only  reason  that  they  failed,  aside  from  the  fact  that  they  were  not 
taking  note  of  the  ultimate  composition  of  the  clays,  was  the  unequal 
degree  of  homogeneity  of  mixture  of  the  fusing  components.  Their 
method  would  have  failed  even  had  the  clays  and  flux  been  ground  and 
mixed  as  thoroughly  as  is  possible  by  any  physical  means  so  far  devised. 
If  they  had  desired  to  be  extravagant  of  time  and  fuel  they  could  have 
caused  their  mixtures  to  fuse  at  the  arbitrarily  chosen  temperatures,  or 
even  lower.  They,  however,  were  not  seeking  to  determine  the  true 
melting  point  of  their  mixture  but  rather  its  refractoriness.  If  they 
had  been  seeking  the  true  melting  point  they  could  have  resorted  to  the 
customary  method  of  noting  the  point  at  wThich  the  fused  mass  solidified. 

Eefractoriness  of  a  clay  is  its  ability  to  withstand  heat  treatment. 
The  relation  between  refractoriness  arid  true  melting  point  of  a  clay 
is  as  difficult  to  trace  as  the  relation  between  refractoriness  and  ultimate 
chemical  composition — if,  indeed,  it  is  not  more  difficult.  This  is  due 
principably  to  the  character  of  the  mineral  aggregate  contained  in  the 
clay. 

In  the  case  of  shales,  the  same  is  true  to  a  very  much  more  marked 
degree.  In  the  shales  the  rate  and  final  attainment  of  fusion  is  af- 
fected so  largely  by  the  character  of  the  mineral,  aggregates  that  we 
find  clays  which  are  serviceable  for  paving  brick  manufacture  differing 
very  greatly  in  physical  properties.  It  is  for  this  reason  in  large  part 
that  coarse-grained  clays  vitrify  more  closely  and  form  stronger  bricks. 
In  fact,  the  writer  does  not  know  of  a  single  factory  in  which  paving 
brick  is  manufactured  from  fine-grained  clays,  although  in  the  labora- 
tory several  fine-grained  clays  have  given  promising  results.  If  there 
is  a  preponderance  of  stable,  not  easily  fusible  minerals  present,  there 
is  no  reason,  so  far  as  the  pyro-chemical  properties  are  concerned,  why 
fine-grained  clays  cannot  be  used  in  the  manufacture  of  paving  brick. 

Tola  tile  Matter — Chemically  combined  water,  carbonic  acid  gas,  car- 
bon, etc.,  do  not  of  themselves,  on  expulsion,  cause  thermo-physical  and 
chemical  reactions  to  take  place  between  the  stable  bases,  acids  and  sili- 
cate compounds  left  behind,  but  their  expulsion  does  involve  changes 
in  physical  and,  in  some  senses,  chemical  conditions  that  provoke 
thermal  reactions  between  the  remaining  substances.  For  example,  in 
terra-cotta  lumber,  sawdust  is  added,  so  that  when  it  burns  out,  the 
mass  will  be  left  extremely  porous,  i.  e.,  not  dense,  as  it  would  otherwise 
have  been.  The  sawdust  in  this  instance  has  been  effective  in  opening 
the  structure  of  the  ware  and  preventing  the  particles  of  clay  from 
coming  within  fluxing  distance  of  one  another  as  they  otherwise  would. 
What  is  true  in  the  case  of  the  sawdust  in  terra-cotta  lumber  is  true 
of  combustible  organic  matter  in  clays.  It  is  obvious,  however,  that  the 
influence  of  carbon  in  this  connection  depends  to  a  very  large  degree 
on  the  size  of  the  carbon  particles. 


238  PAVING    BRICK    AND    PAVING   BRICK   CLAYS.  [bull.  no.  9 

The  effect  of  the  expulsion  of  CO?  from  such  compounds  as  ferrous 
carbonate,  calcium  carbonate,  etc.,  on  the  thermo-chemical  behavior  of 
clays,  is  another  familiar  phenomenon,  the  importance  of  which  is  not 
recognized  in  the  attempt  to  interpret  the  results  of  an  ultimate  chem- 
ical analysis.  If  two  equal  .portions  of  the  same  clay  are  taken,  and  to 
the  one  a  quantity  of  red  iron  oxide  (FeaOs),  while  to  the  other  an 
equivalent  quantity  of  powdered  ferrous  carbonate  (FeCO)  is  added, 
and  the  two  mixtures  burned  under  the  same  thermal  conditions,  it  will 
be  found  that  the  mixture  containing  the  ferrous  carbonate  will  begin 
to  fuse  earlier,  exhibit  a  more  erratic  rate  of  decrease  in  specific  gravity 
as  the  intensity  of  the  heat  increases,  and  may  or  may  not,  depending 
upon  conditions  other  than  those  here  considered,  cause  an  earlier  ulti- 
mate fusion.  The  same  is  true  to  a  greater  or  less  extent  in  the  relative 
fluxing  effect  of  the  oxides  and  carbonates  of  other  bases.  The  same 
phenomena  are  also  notable  in  the  comparative  fiuxing  effect  of  such 
hydrous  and  anhydrous  silicate  compounds  as  raw  and  calcined  kaolin. 

Meade1  and  Meller2  have  shown  that  mineral  mixtures  containing 
alkalies  lose  when  burned  as  high  as  20  per  cent  of  the  total  alkalies 
present.  Such  a  loss  is  bound  to  affect  the  fusibility  of  the  mass  very 
considerably.  Now  we  know  that  the  alkalies  are  less  volatile  when 
combined  with  some  constitutents  than  with  others.  The  amount  of 
alkali  volatilized,  and  hence  the  effect  on  the  fusibility  of  the  clay,  is 
dependent,  therefore,  quite  largely  upon  the  manner  of  its  combination. 

Structure  of  Ware — Intimacy  of  contact  of  the  clay  grains  with  one 
another  is  probably  affected  more  largely  by  the  manner  in  which  the 
mass  is  formed  into  ware  than  by  any  other  factor  within  the  power  of 
man  to  control,  save  the  grinding  of  the  clay.  In  dry-pressed  bricks 
the  clay  particles  are  not  in  such  close  contact  with  one  another  as  they 
would  be  if  the  ware  were  formed  by  the  stiff-mud  method.  In  soft- 
mud  bricks  the  excessive  amount  of  water  used  prevents  the  clay  parti- 
cles from  coming  into  as  intimate  contact  with  one  another  as  in  the  stiff- 
mud  manufacture.  As  a  result  of  these  differences  in  the  degree  of 
compactness  of  the  grains,  it  is  found  that  not  only  a  more  easily  vitri- 
fied and  fused  mass  is  formed,  but  also  that  the  resultant  ware  is  very 
much  stronger  when  made  by  stiff-mud"  methods.  For  the  same  reason 
this  same  difference  is  found  between  the  pressed  and  jiggered  pottery 
wares. 

Material — Calcium  carbonate,  hydrates  of  silica,  alumina,  and  iron, 
as  well  as  zeolitic  compounds,  when  first  precipitated  or  formed,  are  in 
the  majority  of  cases  in  extremely  fine  grains.  The  fiuxing  behavior 
of  any  substance  is  materially  different  when  thoroughly  disseminated 
in  minute  grains,  especially  in  the  colloidal  form,  than  when  present  in 
coarser  grains.  Iron,  for  instance,  has  been  found  to  enter  into  chem- 
ical combination  with  silica  as  a  ferric  silica  when  the  iron  is  precip- 
itated on  flint  and  as  a  ferrous  silicate,  if  at  all,  when  the  two  are 
mixed  as  dry  powders.     The  vast  difference  between  the  fiuxing  action 

1  "Portland  Cement,"  Easton,  Pa.,  1906. 

2  Trans.   Eng.  Cer.   Soc,  Vol.  VI,  p.   130. 


purdyJ  QUALITIES   OF   CLAYS    FOR    MAKING    PAVING    BRICK.  '2M 

of  ferrous  and  ferric  oxides  and.  compounds  need  not  be  discussed  at 
this  time.  The  important  fact  in  this  connection,  is  that  it  depends  to 
a  very  large  extent  on  the  form  and  manner  in  which  the  iron  is  dis- 
seminated through  the  clay,  as  to  whether  it  will  combine  as  the  lower 
or  higher  oxide.  What  is  true  of  iron  in  this  respect  is  true  to  a  degree 
of  other  fluxes. 

Sumnianj  of  Factors  Affecting  Manner  of  Fusion  of  Clays — First — 
The  manner  in  which  the  several  constitutent  elements  are  combined. 
one  with  another,  very  materially  affects  the  fluxing  behavior  of  a  clay. 

Second — The  size  of  grain  of  the  several  mineral  constituents  is  an 
important  factor  in  determining  the  fusing  behavior  of  clays. 

Third — The  amount,  form,  and  character  of  the  volatile  constituents 
of  clay  does  not  directly  affect  the  thermo-chemical  reactions,  but  the 
difference  in  physical  condition  and  structure  of  the  clay,  and  the  sta- 
bility of  the  non-volatilized  compounds,  caused  by  the  expulsion  of 
these  substances,  does  materially  affect  the  manner  in  which  fusion 
takes  place. 

Fourth— The  importance  of  the  role  that  absorbed  salts  play  in  the 
fusing  behavior  of  clays  is  little  appreciated.  The  evidence  on  the 
manner  in  which  they,  operate  is  so  indirect  that  definite  statements  or 
conclusions  are  impossible.  That  they  are  important  factors,,  however, 
there  is  no  doubt. 

Fifth — Concerning  precipitated  materials,  we  have  evidence  from  syn- 
thetical experiments  that  prove  beyond  doubt  that  they  must  be  con- 
sidered as  most  potent  in  affecting  the  fusion  of  clays. 

From  the  above,  it  is  evident  that  the  writer  has  but  little  confidence 
in  the  efficiency  of  an  ultimate  analysis  of  a  clay  as  a  means  of  fore- 
telling its  burning  properties.  The  combination,  size  and  character  of 
grain,  solubility,  volatility,  and  dissemination  of  the  several  salts,  and, 
lastly,  the  manner  in  which  the  uncombined  oxides  are  introduced  into 
the  clay  are  more  effective  factors  than  the  total  ultimate  composition. 

Eelation  of  Chemical  and  Physical  Constitution  to  Behavior 

in  Fusion. 

chemical  composition. 

Historical — Search  in  ceramic  literature  disclosed  the  fact  that  prac- 
tically no  data  have  yet  been  published  that  have  a  direct  bearing  on  the 
relation  of  chemical  and  physical  constitution,  behavior  of  clays  in 
fusion,  and  toughness  of  the  burned  ware.  Ogden1  did  some  prelimin- 
ary work  on  the  relation  of  composition  to  toughness  in  porcelains  and 
found  the  remarkable  fact  that  increase  of  clay  content  from  30  to 
60  per  cent  caused  a  decrease  in  the  toughness  of  porcelain.  Inasmuch 
as  he  employed  the  "rattler  test''  in  determining  relative  toughness  of 

l  Trans.  Am.  Cer.  Soc,  Vol.  VII. 


240  PAVING   BRICK   AND    PAVING   BEICK   CLAYS.  [bull.  no.  9 

his  bodies,  his  studies  are  directly  applicable  to  the  study  of  paving 
brick  clays.  While  the  development  of  toughness  has  not  been  shown 
to  have  a  direct  relation  to  the  rate  and  manner  of  vitrification  except 
in  our  own  results,  yet  that  such  a  relation  exists  can  be  assumed  until 
other  evidence  proves  the  contrary.  If  this  assumption  is  correct,  Og- 
den's  results  would  show  that  the  evidence  developed  by  metallurgists 
to  the  effect  that  addition  of  either  aluminum  oxide  or  silicon  oxide  not 
only  raises  in  degrees  centigrade  the  period  at  which  fusion  is  com- 
pleted, but  also  increases  the  viscosity  of  the  molten  mass,  and  the  rate 
at  which  verification  takes  place,  is  not  applicable  to  certain  mixtures 
It  must  be  admitted  that  before  Ogden  published  his  results,  ceramists 
entertained  the  belief  that  the  greater  the  content  of  AhO  and  SiO* 
in  clays,  the  greater  would  be  the  toughness.  The  findings  in  the  case 
of  fire  clays  here  reported  confirm  Ogden's  ideas. 

In  the  following  paragraphs  will  be  given  such  evidence  as  seems  to 
bear  on  this  point. 

Effect  of  AhO*  in  Ceramic  Mixtures — It  has  been  known  for  some 
time  that  the  addition  of  AI2O3  to  clays  and  clay  mixtures  increases  their 
refractoriness.  Fire  clays,  high  in  AkOs,  are,  as  a  rule,  the  most  re- 
fractory. AI2O3  not  only  raises  the  actual  period  at  which  fusion  is 
completed  but  also  causes  the  wares  made  from  aluminous  clays  to 
soften  and  deform  very  slowly.  The  slower  softening  and  deformation 
of  ware  made  from  aluminous  clays  has  been  attributed  to  increase  of 
viscosity1  of  the  mass  caused  by  alumina. 

The  writer  has  shown2  that  the  addition  of  AI2O3  as  a  constituent  of 
clay  to  stoneware  glazes  until  the  proportion  of  alkali  and  alkaline  earth 
to  alumina  was  2.5  to  1,  not  only  rendered  the  glaze  more  fusible  but 
also  less  viscous.  Additions  of  AI2O3  above  this  proportional  amount  in- 
creased the  refractoriness  of  the  glaze,  if  not  its  viscosity.  Addition  of 
AI2O3  as  a  constituent  of  feldspar  did  not  have  as  great  effect  on  the 
fusibility  of  the  glaze  as  did  the  same  equivalent  of  ALO  from  clay, 
notwithstanding  the  additional  alkali  that  would  be  introduced  by  the 
feldspar. 

From  these  stoneware  glaze  studies  it  was  concluded  that  it  was  not 
so  much  a  question  of  quantity  of  AI2O3,  but  of  the  manner  in  which  it 
was  added.  If  added  as  a  constitutent  of  clay  it  is  already  combined 
with  silica  and  water.  Whether  it  is  this  mutual  solution  of  calcium 
carbonate  and  clay  that  caused  greater  ultimate  fusibility  in  the  stone- 
ware glazes,  when  clay  was  increased  to  a  definite  amount,  or  whether 
it  was  a  complex  case  of  an  eutectic  mixture  of  several  substances,  is 
not  yet  determined.  The  fact  remains  that  additon  of  clay  did  cause 
greater  fusibility  and  less  viscosity,  notwithstanding  the  fact  that  with 
each  addition  of  clay  the  AhOs  was  being  increased. 

Bleininger3  has  shown  experimentally  that  calcium  carbonate  reacts 
with  finely  pulverized  feldspar  as  readily  as  with  washed  kaolin.  From 
his  results  it  would  seem  as  though  fusion  is  initiated  between  calcium 

1  Molasses  is  more  viscous  than  water,  i.  e.,  it  flows  more  sluggishly.     Its  mole- 
cules are  less  free  to  move.     Slow-flowing  fluids  are  said  to  be  viscous. 

2  Trans.  Am.  Cer.   Soc,  Vol.  V. 

SGeol.  Surv.  of  Ohio,  Bull.  No.  3,  4th  series,  p.  128. 


puri.vI  PYEO-PHYSICAL    AND   CHEMICAL    PROPERTIES.  .    241 

carbonate  and  feldspar  as  early  as  between  calcium  carbonate  and  kaolin 
(pure  clay).  This  being  the  case  it  would  seem  as  though  the  addition 
of  clay  to  stoneware  glaze  mixtures  was  merely  the  formation  of  a 
eutectic  mixture  of  minerals.1 

Kvidence  thus  far  developed  in  the  case  of  simple  mixtures  is  sum- 
marized in  the  following  table: 

TABLE  XXXI. 

Showing  the   proportions  by  weight,  which  cause  maximum   fusibility   between 
the  two  mineral  substances  stated  in  each  case. 

.    (1)  (2) 

(1)      Magnesium  carbonate    (1)    and  kaolin    (2)    2 

Calcium  carbonate    (1)    and  kaolin    (2)    2 

Finely  pulverized  flint   (1)   and  kaolin   (2)    2  7 

Finely  pulverized  flint   (1)   and  feldspar   (2)    1  3 

(1)      With  quick  fire. 

Any  increase  or  decrease  of  AhO  outside  of  the  limits  given  in  the 
above  table  results  in  increase  of  refractoriness  of  the  mixtures  as 
shown  in  the  several  curves  to  which  reference  has  been  made:  Similar 
points  of  greatest  fusibility  have  been  noted  in  the  case  of  glazes,  but 
data  have  not  been  obtained  that  permit  showing  the  facts  in  tabular 
or  curve  form.  AhO  then  increases  the  fusibility  of  mineral  mixtures 
when  added  in  amounts  not  exceeding  a  given  proportional  limit,  the 
limit  being  different  for  different  mixtures. 

Second,  in  slags,  glazes  and  glasses  addition  of  AhOs  above  a  given 
amount  increases  their  viscosity^,  but  no  limiting  points  have,  as  yet,  been 
determined  except  # in  the  case  of  slags.  Since  slags  are  comparatively 
simple  in  composition  and  usually  relatively  high  in  lime,  we  can  learn 
very  little  by  reviewing  in  detail  the  researches  that  have  been  made 
on  the  vicosity. 

Third — Increase  of  AkOs  in  small  amount  in  glasses  increases  their 
toughness.  So  far  as  data  have  been  obtained  increase  of  AhO  in  por- 
celain bodies  does  not  increase  their  toughness. 

From  these  conclusions  a  query  is  at  once  presented  concerning  the 
relation  between  fusibility,  viscosity  and  toughness.  At  present  any  dis- 
cussion of  this  query  would  be  based  wholly  on  assumption,  for  there 
are  no  experimental  data  bearing  on  the  point. 

Effect  of  Silica  in  Ceramic  Mixtures — Anhydrous  silica  is  practically 
inert  at  ordinary  temperatures,  but  at  the  temperature  usually  attained 
in  brick  kilns  it  becomes  very  active,  forming  compounds  having  very 
varied  oxygen  ratios,  i.  e.,  amount  of  oxygen  in  the  basic  to  the  oxygen 
in  the  acid  oxides. 

On  heating,  silica  expands  considerably,  indicating  peculiar  molecu- 
lar  changes.     LeChatelier2   has  shown*  that  at   500 °C.   this   molecular 

1  The    mixtures    that    gave   the    greatest    fusibility,    as    shown    in    each    of   the 
figures  19,  20  and  21,  are  said  to  be  eutectic  mixtures. 

2  See  Bleininger,   Ohio  Geol.   Surv.,  Bull.  3,  p.   28. 


-1G  G 


242 


PAVING   BRICK   AND    PAVING    BRICK   CLAYS. 


[BULL.    NO.    9 


change  takes  place  to  a  very  pronounced  degree  in  all  forms  of  silica, 
the  least  in  amorphous  and  the  most  in  highly  calcined  flint.  Per- 
manent expansion  in  highly  silicious  bricks  and  the  "punkness"  of  bricks 
made  from  a  mixture  of  clay  and  sand  are  evidence  of  the  effect  of  this 
peculiar  property  of  silica. 

No  matter  how  fine  the  free  silica  is,  it  does  not  seem  to  be  as  active  in 
forming  new  silicate  compounds  under  the  influence  of  heat  as  is  the 
silica  that  is  previously  combined,  as  for  illustration,  in  clay  or  feldspar. 
In  other  words,  silicate  combination  with  free  basic  elements  is  affected 
more  readily  when  the  silica  is  added  to  the  mixture  as  a  constitutent 
of  a  pre-existing  silicate.  This  was  shown  very  prettily  in  an  experi- 
ment reported  by  Bleininger.1  He  prepared  a  mixture  of  20  per  cent 
finely  ground  flint  and  80  per  cent  precipitated  calcium  carbonate  and 
two  other  mixtures  each  containing  respectively  20  per  cent  finely 
ground  feldspar  and  20  per  cent  of  kaolin  with  80  per  cent  calcium  car- 
bonate. These  mixtures  were  maintained  at  a  temperature  of  1100  C. 
for  75  minutes.  At  this  temperature  calcium  silicate  compounds  are 
formed  which  are  soluble  in  hot  hydrochloric  acid  and  sodium  carbonate 
solutions.  The  residue  left  after  this  acid  and  alkali  treatment  is  the 
material  which  is  unattacked  or  unlocked  by  the  fluxing  action  of  the- 
lime.     In  the  following  table  are  Bleininger's  results. 

Table   XXXII. 


Ground 
Flint. 

Ground 
Feldspar. 

Ground 
Kaolin. 

Per  cent  residue 

28.83 

3.75 

3.07 

Per  cent  taken  into  solution * 

71.17 

96.25 

96.63 

Bleininger's  results  strongly  support  the  doctrine  that  has,  for  the 
sake  of  emphasis,  been  repeatedly  stated  in  this  report,  to-wit:  That 
very  little  can  be  told  concerning  the  fusing  behavior  of  silicate  mix- 
tures from  an  ultimate  analysis,  for  if  this  were  not  the  case,  feldspar 
should  have  reacted  far  more  vigorously  with  calcium  carbonate  than 
did  clay.  Since  cement  investigators  have  found  that  the  hydrous  am- 
orphous silica  reacts  with  lime  in  a  manner  similar  to  finely  pulverized 
crystalline  quartz,  it  can  be  readily  seen  that  misleading  data  would  be 
obtained  even  in  the  rational  analysis,  in  which  the  hydrous  amorphous 
silica  is  taken  into  solution  by  the  sulphuric  acid  and  thus  considered  as 
a  part  of  the  clay  substance. 

Addition  of  silica  to  pure  clays  like  shales  increases  their  refractori- 
ness and,  (reasoning  from  data  on  slags)  possibly,  their  viscosity.  There 
is  no  evidence  showing  that  the  addition  of  flint  to  a  clay  increases  its 
toughness,  but  quite  the  contrary,  empirical  experiments  by  several  prac- 
tical brick  manufacturers  have  proved  that  the  additon  of  ordinary  bank 
sand  makes  the  bricks  less  tough  or  even  very  "punky."  On  the  other 
hand  an  investigation  by  Worcester2  proved  that  Bedford  shale,  which 

1  Loc.  cit..  p.  128. 
2  Trans.   Am.   Cer.   Soc.  Vol.  II,  pp.   295. 


PURDY]  PYRO-PHYSICAL    AND    CHEMICAL    PROPERTIES.  243 

outcrops  near  Columbus,  0.,  is  materially  benefitted  by  an  addition  of 
crushed  Berea  sandstone  from  the  same  locality.  Instances  are  recorded 
of  addition  of  certain  sands  in  Europe  having  proved  beneficial, -but  in 
neither  Worcester's  experiments  nor  in  the  European  cases  was  there 
reported  a  determination  of  the  effect  of  sand  on  the  toughness  of  the 
burned  mixtures. 

In  the  manufacture  of  floor  tile  the  writer  found  that  a  porcelain 
body  consisting  of  40  per  cent  clay,  45  per  cent  feldspar  and  15  per  cent 
flint  was  much  tougher  than  a  body  containing  35  per  cent  clay  and  65 
per  cent  feldspar.  It  is  impossible  to  say  why  the  body  containing  flint 
should  be  tougher  but  certainly  some  credit  must  be  given  to  the  influ- 
ence of  the  flint. 

Eeviewing  the  known  facts  about  the  effect  of  silica  on  either  the 
fusion  of  clays  or  development  of  toughness  in  clay  wares,  it  must  be 
admitted  that  we  have  not  at  present  much  positive  evidence. 

Effect  of  Magnesium  Oxide  in  Ceramic  Mixtures — In  figure  20  on 
page  209  is  shown  graphically  in  fluxing  effect  of  magnesium  oxide 
with  kaolin.  Metallurgists  report  that  magnesium  oxide  is  a  much 
"harder"  flux  than  calcium  oxide  and  produces  a  much  more  viscous 
slag.  Ceramic  investigators  have  reported  conflicting  results  in  their 
attempts  to  use  MgO  as  a  flux,  some  claiming  that  it  is  more  active  than 
CaO  and  some  that  it  is  less  active.  Claims  have  been  made  by  some 
that  in  glazes  it  gives  greater  fusibility  and  slower  fusion,  while  others 
claim  opposite  results.  From  this  accumulation  of  apparently  conflict- 
ing data  it  has  been  shown  that  in  short  quick  burns,  as  in  experimental 
kilns,  MgO  is  an  active  flux  causing  more  rapid  fusion,  but  in  longer 
burns  its  fluxing  action  begins  as  early  as  in  the  shorter  burns  but  pro- 
gresses less  rapidly  and  requires  more  intense  heat  treatment  to  effect 
complete  fusion. 

The  lag  in  the  fusion  of  mixtures  containing  magnesium  oxide  is  at- 
tributed to  either  the  viscosity  of  the  resulting  magnesium  silicate,  if 
it  enters  into  combination  with  the  glassy  matrix  that  fills  and  seals  the 
pores  of  vitrifying  wares,  or  to  the  formation  of  non-fluid  magnesium 
compounds.1  Cement  investigators  claim  that  the  alkaline  earth  sili- 
cates formed  by  heating  mixtures  of  clay  and  calcium  or  magnesium  car- 
bonate at  temperatures  below  that  required  to  cause  sintering  of  the 
mass  into  a  hard  cake  or  brick  are  simple  silicates  of  calcium  or  mag- 
nesium oxide  which  are  not  necessarily  fluid.  At  any  rate,  the  effect 
of  magnesium  in  ceramic  mixtures  differs  from  that  of  calcium  in  that 
the  magnesium  mixtures  fuse  very  slowly  over  a  long  heat  range,  while 
the  calcium  mixtures,  especially  when  present  in  amounts  equal  to  or 
more  than  10  per  cent,  remain  porous  up  to  the  time  that  fusion  begins, 
and  then  fluxing  ensues  very  rapidly  causing  the  ware  to  pass  from  por- 
ous into  the  overburned  condition  within  a  very  short  range  of  heat 
treatment. 


l  Eckel  states  in  "Cements,  Limes  and  Plasters,"  p.  154,  that  when  magnesia 
is  burned  in  a  quick  fire  its  density  (specific  gravity)  is  3.0  to  3.07,  while  if 
burned  in  a  slow,  long-continued  fire  its  specific  gravity  will  range  from  3.6  to  3.8. 


244  PAVING    BRICK    AND    PAVING    BRICK   CLAYS.  [bull.  no.  9 

The  only  known  facts  concerning  the  influence  of  magnesium  oxide  in 
ceramic  mixtures  are  :  (1)  magnesium  oxide  increases  viscosity;  (2)  mag- 
nesium oxide  causes  slower  rate  of  fusion,  at  least  when  it  is  the  pre- 
dominating flux;  (3)  as  has  been  stated  earlier  in  this  report,  clays 
which  make  good  paving  bricks  contain  a  larger  amount  of  magnesium 
than  calcium  oxide;  (4)  the  Italians  are  now  making  low-fired  porce- 
lain of  which  toughness  is  a  special  feature,  and  in  which  magnesium  is 
the  only  Ro  or  fluxing  base  present. 

Effect  of  Calcium  Oxide  in  Ceramic  Mixtures — Watts1  has  shown  that 
the  presence  of  a  small  amount  of  calcium  oxide  in  porcelain  mixtures 
results  in  increased  toughness  of  the  ware.  His  investigations  are  not, 
however,  sufficiently,  exhaustive  to  warrant  more  definite  statement. 

It  is  known  that  lime  causes  a  breaking  down  of  the  silicates  with 
comparatively  little  heat  treatment,  and'  also  that  the  new  silicates 
formed  are  probably  very  simple  in  composition  until  higher  tempera- 
tures are  attained,  in  which  event  these  simple  silicates  suddenly  fuse, 
causing  the  whole  to  pass  rapidly  into  a  fluid  mass. 

Dr.  Rieke2  has  shown  that  in  mixtures  of  from  1  to  10  per  cent  of 
calcium  carbonate  with  kaolin  very  close  tight  bodies  are  obtained  which 
have  quite  a  large  range  of  vitrification  and  in  the  end  fuse  quite 
gradually.  Mixtures  containing  more  than  10  per  cent  of  calcium  car- 
bonate remain  quite  open  until  final  fusion  begins,  at  which  time  the 
whole  mass  fuses  very  rapidly. 

In  comparison  with  Rieke's  work  it  is  of  interest  to  study  results 
obtained  by  Nauss,3  who  worked  with  a  mixture  similar  to  Rieke's  high 
calcium  body. 

The  two  bodies  were  as  follows : 

Tam.e   XXXIII. 


Nauss. 

Rieke. 

Calcium  carbonate 

70 

11.05 

18.66 

70 

Kaolin 

30 

Flint  

In  the  following  table  are  Nauss'  results  and  in  a  separate  column 
are  placed  the  data  obtained  by  Rieke.  Rieke  measured  his  heat  by  cones 
and  hence  the  temperatures  obtained  in  these  two  studies  cannot  be  com- 
pared closely.  Since,  however,  Rieke  used  a  Seger  trial  kiln  and  very 
short  firing  periods,  his  cone  readings  can  be  approximated  in  terms 
of  degrees  centigrade  within  the  accuracy  of  and  discrepancy  between 
the  method  by  which  each  research  was  executed. 

l  Trans.  Am.  Cer.   Soc,  Vol.  V,  pp.   175. 

2  Sprechsaal  No.  38,   1906. 

3  Reported  by  Bleininger,  Ohio  Geol.  Surv.  Bull.  No.  3,  p.  175. 


PURDYj 


PYRO-PHYSICAL    AND    CHEMICAL    PROPERTIES. 


245 


Table  XXXIV. 
Reaction  of  Calcium  Oxide  upon  Kaolin  and  Quartz. 


2 

• 

IB 

3 

0 

n 

r 

o 

CO 
CO 

O 
D 

er 

e 

3 
5' 

r 

3  co 

P8 

:  3 

•  H. 
;  n 
'.    n 

o 

=  5- 
S.§ 
3.O. 

o  c 

ft   CO 

':  <* 

•  CO 

■    o' 
.    » 

:    1 

•  X) 

Remarks. 

RlEKE'S 

Results. 

( 

o 
o 

co_ 

n 

fa 

0Q 

1 

550 

585 

610 

655 

700 

725 

750 

775 

800 

850 

900 

950 

1000 

1050 

1100 

1150 

1150 

1200 

1200 

1250 

1250 

1300 

1300 

1325 

1.79 

1.88 

1.80 

1.91 

4.81 

6.18 

6.99 

8.35 

12.51 

20.34 

24.42 

27.56 

30.00 

29.75 

29.65 

29.74 

30.10 

30.10 

30.10 

30.10 

30.10 

30.10 

30.10 

30.10 

27.79 
27.96 
28.67 
28.83 
25.17 
24.30 
23.02 
21.90 
17.94 
10.64 
5.89 
2.88 
0.60 

28.48 
28.44 
28.84 
27.83 
25.89 
24.58 
23.88 
21.07 
18.72 
7.32 
5.29 
2.17 
0.40 

2 

3 

4 

5  - 

6 

7 

8 

19.70 

9 

10 

19.00 

11 

12 

18.90 
18.83 
18.75 
18.75 
18.26 
16.19 
16.10 
15.37 
13.13 
13.34 
11.97 
10.68 

13 

14 

30.3 

05 

15 

16 

17 

Held  at  this  temperature  for  12  hours. .. 

42.5 

2 

18 

19 

45.9 

5 

20 

21 

22 

Dusted 

42.0 

8 

23 

24 

Began  to  fuse,  "melt"  

10.2 

Fused. 

10 

lb      ... 

23-24 

Professor  Bleininger's  conclusions  from  Nauss^  work  are : 

"First — In  regard  to  the  decomposition  of  calcium  carbonate,  it  is  clearly 
shown  that  it  begins  to  break  up  between  610°  and  650°C,  and  before  700° 
is  reached  the  evolution  of  carton  deoxide  is  going  en  quite  rapidly.  At 
1000°  the  evolution  is  practically  at  an  end." 

"Second — On  examining  the  amounts  of  insolublei  residue  and  comparing 
the  percentage  with  the  known  amount  of  quartz  in  the  mixture,  18.66  per 
cent,  and  making  allowance  for  the  small  amount  of  quartz  in  the  kaolin 
itself,  it  is  seen  that  the  kaolin  is  decomposed  completely  at  850°C,  and  al- 
most completely  at  800°C." 

'  Third — Free  quartz  seems  to  be  attacked  by  the  calcium  oxide  soon  after 
the  completion  of  the  decomposition  of  kaolin,  probably  at  about  950°C, 
which  reaction  continues  at  an  increasing  rate  up  to  the  highest  tempera- 
ture employed  in  these  experiments.  It  is  quite  evident,  also,  that  the  length 
of  time  of  burning  influences  the  amount  of  quartz  attacked  somewhat,  so 
that  by  longer  burning,  at  least  with  temperature  over  1100°,  more  quartz 
may  be  rendered  soluble  than  in  a  short  period  of  ignition." 

Prof.  Bleininger,  continuing,  says: 

"A  very  interesting  fact  was  brought  out  by  the  tendency  to  dust  observed 
with  the  mixture  at  temperatures  above  1200°C.  While  at  1200°  the  bri- 
quettes were  hard,  at  1250°  they  dusted  very  rapidly,  and  at  1300°  almost 
instantaneously." 


l  Insoluble  in  hydrochloric  acid  and  sodium  carbonate  solutions. 


24()  PAVING    BRICK    AND    PAVING   BRICK   CLAYS.  [bull.  no.  9 

"On  calculating  the  formula  of  this  mixture  from  the  composition  we  find 
it  to  be  1.77  CaO,  0.108  AL>03,  Si02,  that  is  not  quite  a  singulo  calcium  sili- 
cate, and  hence  must  properly  be  classed  within  the  group  of  natural  ce- 
ments. It  is  not  difficult  to  understand  that  the  dusting  must  be  coincident 
with  a  significant  molecular  change  from  the  condition  of  the  loose,  friable 
mixture  to  a  hard  body  breaking  down  at  once  to  a  powder.  Might  not  this 
fact  indicate  that  up  to  1200°  these  calcareous  mixtures  are  but  pozzuolane- 
like,  simple  silicates,  consisting  of  silica  and  base  which  on  further  applica- 
tion of  heat  become  chemically  more  complex  and  non-or  but  slightly  hy- 
draulic? This  view  is  strengthened  by  the  results  of  another  investigation 
which  have  shown  that  on  increasing  the  free  silica,  with  but  sufficient  base 
to  convert  the  quartz  into  the  active  state,  the  hydraulicity  is  practically  as 
great  as  with  a  greater  amount  of  base."i 

Eieke's  data  is  evidence  that  Bleininger's  query  can  be  answered  in 
the  affirmative,  for  it  was  at  this  same  temperature,  1200 °C.,  that  his 
body  ceased  to  increase  in  porosity  and  began  to  vitrify.  From  1200°  C. 
onr  Eieke's  body  vitrified  quite  rapidly  showing  that  "a  significant 
molecular  change"  is  taking  place.  From  Nauss'  results  it  must  be 
conceded  that  the  clay  has  suffered  a  very  significant  change.  Nf> 
doubt  it  has  passed  completely  into  solution  with  lime  and  silica.  In 
fact  Bleininger's  results  given  in  Table  XXXVI  page  248  proves  this 
to  be  so. 

Eieke's  porosity  data  show  also  that  prior  to  this  critical  tempera- 
ture, 1200°,  (rough  approximate)  the  grains  must  be  changing  form 
and  size,  for  the  mass  is  getting  more  porous  with  each  increase  in  heat 
treatment,  yet,  according  to  his  shrinkage  data  (1.2  per  cent  at  cone 
05  and  3.7  per  cent  at  cone  5)  the  mass  as  a  whole  is  decreasing  in  vol- 
ume. Similar  simultaneous  increase  in  porosity  and  decrease  in  volume 
was  noted  in  several  instances  in  our  own  researches,  so  this  phenom- 
enon is  not  alone  peculiar  to  simple  mixtures  high  in  lime. 

Important  as  are  these  observations,  and  especially  that  of  complete 
solution,  and  possibly  the  formation  of  entirely  new  compounds  before 
the  mass  begins  to  decrease  in  porosity,  i.  e.,  vitrify,  the  more  important 
item  to  note  at  this  time  is,  in  the  writer's  opinion,  the  difference  in 
the  ultimate  fusion  behavior  of  the  two  bodies,  the  one  containing  fre£ 
silica  and  the  other  supposedly  none.  It  was  shown  by  Bleininger's 
result2  that  quartz  is  not  nearly  as  readily  attacked  by  CaO  as  is  kaolin 
or  feldspar,  and  hence  it  could  be  inferred  that  the  higher  the  content 
of  quartz  in  a  mixture,  the  later  and  slower  would  the  mass  fuse.  In 
decided  contradiction  to  such  an  inference  we  find  that  in  Xauss'  body, 
containing  18.7  per  cent  quartz,  the  original  minerals  have  been  com- 
pletely broken  down  and  the  whole  began  to  "melt"  at  the  same  tem- 
perature at  which  Eieke's  body  containing  no  quartz  exhibits  a  porosity 
of  10  per  cent,  but  complete  fusion  does  not  take  place  until  a  tem- 
perature of  about  1600°  C.  has  been  reached.  We  are  learning  not  to 
wonder  at  such  apparent  discrepancies  in  experimental  work  where 
simple  mixtures  of  two  minerals  are  compared  in  their  fusing  behavior 
with  more  complicated  mixtures  of  minerals. 

l  Italics  not  in  the  original. 
2  See  Table  XXXVI  p.  248. 


purdy]  PYR0-PHYS1CAL    AND   CHEMICAL    PROPERTIES.  247 

Summarizing  these  observations  the  following  facts  appear:  First, 
Watts  has  shown  that  a  small  quantity  of  lime  toughens  a  porcelain 
mixture.  Second,  Rieke  has  shown  that  in  a  simple  mixture  of  kaolin, 
and  1  to  10  per  cent  calcium  carbonate  there  is  quite  a  large  vitrification 
range  and  slow  fusion,  while  in  mixtures  with  kaolin  containing  more 
than  10  per  cent  of  calcium  carbonate  the  body  does  not  vitrify  until 
late  and  then  rather  suddenly  fuses.  These  findings  by  Rieke  and 
Watts  agree  with  ours  in  support  of  the  assumption  that  long  vitrifica- 
tion range  and  slow  fusion  generally  result  in  the  production  of  tough 
ware.  Third,  the  results  of  Bleininger,  Nauss  and  Rieke  studied  to- 
gether show  very  forcibly  that  chemical  alterations  and  reactions  may 
take  place  long  before  vitrification  and  fusion  begin.  Also,  that  each 
mixture  has  its  own  peculiar  pyro-chemical  and  physical  behavior,  and, 
as  the  mixtures  become  complicated  in  composition,  the  deductions 
drawn  from  simple  mixtures  are  found  to  hold  true  only  in  very  small 
part. 

Beyond  these  studies  in  simple  mixtures  by  Bleininger,  Nauss,  and 
Rieke.  and  the  observation  in  complicated  porcelain  mixtures,  we  have 
no  data  that  have  a  bearing  on  the  effect  of  smaller  or  larger  quantities 
of  lime  on  toughness  of  burned  wares  made  from  shales.  Contrasting 
the  work  of  Rieke  and  Nauss,  the  difficulties  that  are  encountered  when 
attempt  is  made  to  trace  the  effect  of  lime  in  such  severely  complicated 
mixtures  as  shales  are  clearly  shown. 

Effect  of  Oilier  Oxides  in  Ceramic  Mixtures — Practically  nothing  is 
known  concerning  the  influence  of  oxides  other  than  those  considered 
above,  except  that  in  slags  titanium  causes  increased  viscosity;  that 
potash  silicates  are  more  fluid  than  soda  silicates,  and  yet,  as  a  rule, 
less  fusible;  that  phosphoric  acid  is  expelled  from  ceramic  mixtures 
only  at  high  temperatures,  and  that,  before  expulsion  it  is  combined 
with  the  bases  forming  phosphates  that  are  analogous  to  the  silicates. 
A  detailed  study  of  the  influence  of  the  several  oxides,  alone  and  to- 
gether, on  the  fusion  of  silicate  mixtures  and  the  toughness  of  the 
burned  mixtures,  offers  a  very  fruitful  and  interesting  field  for  re- 
search. 

INFLUENCE    OF    SIZE   OF    GRAIN    ON    THE   FUSION    OF    CLAYS. 

Direct  evidence — According  to  Wegemann's  microscopic  studies  given 
on  later  pages,  coarse  quartz  does  not  enter  into  the  fluxing  reactions 
even  at  cone  5.  With  a  heat  treatment  sufficient  to  fuse  cone  5  feldspar 
is  completely  fused  especially  if  mixed  with  free  silica,  and  yet  at  this 
cone  Wegemann  reports  that  the  quartz  grains  are  apparently  unaf- 
fected to  any  noticeable  extent  until  cone  9  is  fused  down.  He  affirms 
that  if  any  reaction  has  taken  place  between  the  free  silica  and  feldspar, 
the  silica  must  have  been  supplied  from  what  he  terms  the  ground 
mass,  i.  e.,  the  mass  that  consists  of  particles  too  fine  to  be  distinguished 
through  the  microscope.  According  then  to  Wegemann's  studies,  the 
melting  feldspar  in  shales  affects  the  coarse  flint  to  but  a  slight  extent. 

Bleininger1  experimentally  determined  the  effect  of  size  of  flint  and 
feldspar  grains  on  the  rate  at  which  lime  would  decompose  them  at 
1100°  C,  forming' silicates  that  could  be  dissolved  in  hydrochloric  acid 


248 


PAVING   BRICK    AND    PAVING   BRICK    CLAYS. 


[BULL.    NO.    9 


Tap,  Lie     XXXV. 
Effect  of  Size  of  Grain  on  Extent  and  Rate  of  Combination  of  Silicia  and  Lime. 


Sizes. 

Ground 
Flint. 

150-120 
mesh. 

120-100 
mesh. 

100-80 
mesh. 

80-60 
mesh. 

60-40 
mesh. 

40-20 
mesh. 

• 

28.83 

63.8 

78.53 

86.52 

86.27 

93  78       96  83 

Per  cent  taken  into  solution 

71.17 

36.2 

21.47 

13.48 

13.73         6.27         3.17 

1 

Table  XXXVI. 

Effect  of  Size  of  Grain  on  Extent  and  Rate  of  Combination  of  Feldspar 

and  Lime. 

Sizes. 

Ground 
Feldspar. 

150-120 
mesh. 

120-100 
mesh. 

100-80 
mesh. 

80-60 
mesh. 

60-40 
mesh. 

40-20 
mesh. 

3.75 

15.45 

31.00 

64.29 

79.63 

95.72 

Per  cent  taken  into  solution 

96.25 

84.55 

69.00 

35.71 

20.37 

4.28 

1 

and  sodium  carbonate.     The  data  he  obtained  are  given  in  the  follow- 
ing tables: 

This  data,  together  with  WegemannV  microscopic  observations,  proves 
conclusively  that  a  variation  of  this  physical  factor — fineness  of  grain 
— has  an  influence  on  the  fusing  behavior  of  clays  that  is  as  positive,  if 
not  as  potent,  as  a  variation  in  the  quantity  of  the  oxides  of  any  of 
the  elements. 

GENERAL  ANALYSIS  OF  RESULTS. 

The  foregoing  detailed  discussion  of  the  various  elements  affecting 
the  manner  in  which  silicate  mixtures  fuse,  has  been  given  in  addition 
to  the  more  general  statements  on  pages  2L7  and  232  so  as  to  make 
more  plain  the  deductions  that  are  to  be  drawn  from  our  own  data. 
This  detailed  citation,  it  is  hoped,  has  clearly  demonstrated  that  our 
present  knowledge  of  the  influence  of  the  several  factors  even  in  simple 
mixtures  is  very  fragmentary  and  that  in  the  more  complex  mixtures  the 
evidence  is,  in  the  main,  either  conflicting  or  entirely  lacking.  In  the 
following  analysis  of  the  chemical  data  obtained  by  this  Survey,  and  at- 
tempts to  show  a  relation  between  the  chemical  and  physical  constitution 
of  the  clays,  their  pyro-physical  behavior,  and  toughness  of  the  burned 
bricks,  liberal  assumptions  must  be  made  and  only  general  conclusions,  if 
any,  drawn. 

These  assumptions  are :  First,  Those  elements  which  are  supposed  to 
increase  the  viscosity  of  the  mass  when  fused  lengthen  the  vitrifying 
range  of  the  clay  and  increase  the  toughness  of  vitrified  wares.  Sec- 
ond, Those  chemical  or  physical  factors  which  tend  to  make  the  mass 
more  fusible  or  to  hasten  the  pyro-chemical  reactions  which  result  in 
vitrification  are  detrimental  to  development  of  toughness.     Third,  That 

lLoc.  cit.  p.  127. 


PUKDVj 


I'YKO-rilYSlCAL    AND    CHEMICAL    PROPERTIES. 


249 


lime  is  detrimental  both  to  slow  fusion  and  toughness,  while  inagnesia 
is  beneficial.  Fourth,  That  the  higher  the  acid  content,  or  its  equivalent, 
the  oxygen  ratio,  the  more  viscous  will  he  the  fused  ingredients  and  the 
tougher  the  burned  ware.  Fifth,  The  higher  the  proportion  of  AbOs 
to  other  basic  oxides  the  slower  will  be  the  fusion,  the  more  viscous  the 
fused  ingredients  and  the  tougher  the  mass.  Sixth,  The  finer  the  ma- 
terial of  which  clay  is  composed,  the  more  rapidly  will  it  fuse  and  the 
more  brittle  will  be  the  burned  mass. 

In  the  following  table  will  be  found  the  ratio  mentioned  in  the  fore- 
going assumptions,  as  calculated  from  the  chemical  data  given  on  pages 
215  and  216.  In  the  first  column  is  the  ratio  of  CaO  to  MgO.  In  this 
ratio,  CaO  is  taken  as  unity.  In  the  second  column  is  given  the  total 
oxygen  in  the  basic  oxides  where  AbO  is  unity. 

In  summing  up  the  oxygen  atoms,  the  iron  oxides  were  considered  as 
reported ,  i.  e.,  where  FeO  is  given,  only  one  atom  of  oxygen  to  one 
atom  of  Fe,  and  where  Fe^O  is  given,  three  atoms  of  oxygen  to  two 
atoms  of  Fe  were  taken.  The  difference  between  the  value  given  in 
tlu-  second  column  and  3    (oxygen  in  AbO)    gives  the  factors  for  the 

Table  XXXVII. 


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3.22 

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2.35 

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2.23 

2.17 

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2.36 

2.10 

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15.82 
17.48 
24  89 
19.11 
19.36 
13.25 
13.89 
20.23 
14.84 
39.36 
28.13 

K—  2 

Good  red  when  vitrified 

K-  3 

K-  i 
K- 
K—  I 

t 

Not  screened  when  used  at  factory 

..do 

K—  7 

K—  8 

K-  9 

K— 10 

Very  hard  coarse  clay 

K— 11 

K-12 

K— 13 

31.50 
21.24 
18.44 
20.84 
26  25 

K-14 

K— 15 

Very  hard  coarse  clay 

F-  1 

S  —  1. 

S  -  2 

27.94 
16.92 
17.80 
14.80 
15.33 

R—  1 

397 

16.5 

No.  2  Fire  clay 

R—  2 

R—  3 

291 
275 

6.55 
8.45 

R—  4 

H-16 

H— 17 

H— 18 

444 

553 
783 
634 

0.39 
0.42 
0.27 
0.53 

H— 20 

H— 21...... 

H— 23 .. 

B— 11..     . 

28.03 
14.98 
32.97 
25.65 
17.14 
18.58 

G-II 

H— 11  .. 

366 

2.3 

Good  dark  red  when   vitrified 

I  —II 

J— II.... 

489 

1.16 

Brighfc  red  when  vitrified 

L— IT 

250  PAVING    BRICK    AND    PAVING   BRICK   CLAYS.  [bull.  no.  9 

proportion  of  oxygen  in  AM);  to  oxygen  in  the  other  bases,  i.  e.,  (a — 3)  : 
:>::(.)  in  fluxes:  ()  in  AUK  in  the  third  column  is  given  the  number 
of  atoms  of  oxygen  in  total  SiOs.  In  the  fourth  column  is  given  the 
ratio  between  oxygen  in  SiO?  to  oxygen  in  total  bases.  This  ratio  is 
known  as  the  oxygen  ratio  and  is  customarily  taken  as  the  ratio  of  the 
acids  to  the  bases.  In  the  fifth  column  is  given  the  surface  factor  rep- 
resenting fineness  of  grain  by  the  writer's  method.     In  the  sixth  col- 

A.  B.  C. 

umn  is  a  modulus  calculated  on  the  formula =  M  where 

D. 
"A"  is  the  lime-magnesia  ratio,  "B"  the-  total  oxygen  ratio,  "C"  the 
ratio  of  oxygen  in  the  Eo  bases  to  oxygen  in  AbOs,  and  "D"  the  sur- 
face factor  divided  by  100.  In  the  seventh  column  is  given  the  rattler 
loss  determined  on  commercially  manufactured  blocks  made  from  each 
clay. 

Deductions  Drawn  from  Table  XLI — Without  going  into  details  con- 
cerning the  probable  reason  for  the  lack  of  correlation  between  the  chem- 
ical and  physical  constitution  and  the  toughness  of  the  burned  ware 
as  shown  in  the  above  data,  it  is  sufficient  to  state  that  it  be  granted 
that  these  data  corroborate  those  of  Ogden,  proving  that  our  notions 
about  the  relation  of  the  chemical  and  physical  constitution  of  clays 
to  the  toughness  that  is  developed  in  burning  are  in  the  main,  if  not 
wholly,  erroneous.  Data  on  mineralogical  composition  as  obtained  by 
the  Rational  Analysis,  gave  results  that  were  still  less  easily  correlated 
with  data  on  toughness  of  the  burned  ware  than  are  those  in  the  above 
table.  Before  such  data  can  possibly  be  of  value  there  must  be  consider- 
ably more  learned  concerning  the  fusing  behavior  and  the  physical  prop- 
erties of  sintered  masses  of  simple  mixtures  of  minerals.  There  is  not 
much  of  any  hope  of  learning  much  concerning  these  relations  from 
data  obtained  by  any  process  of  chemical  analysis  now  used. 

THERMO-CHEMICAL    AND    PHYSICAL    CHANGES    DURING    FUSION. 

It  is  indeed  very  difficult,  if  not  impossible,  to  determine  what  the 
actual  thermo-chemical  reactions  really  are,  which  take  place  in  the 
fusion  of  the  clay  particles,  first  between  themselves,  and,  secondly, 
when  the  whole  mass  becomes  a  more  or  less  homogeneous  solution.1 
By  the  aid  of  the  microscope,  as  will  be  seen  later,  more  can  be  told  con- 
cerning these  changes  in  an  unknown  mixture  of  minerals  than  by  any 
other  means;  inferences  from  artificial  and  known  mixtures  being  of 
no  avail.  The  effect  of  thermo-chemical  reactions,  however,  can  be 
detected  by  the  changes  in  porosity  and  specific  gravity.  Because  of  our 
present  inability  to  ascertain  in  full  the  reactions  that  take  place,  it 
seems  best  to  refer  to  the  chemical  phases  of  fusion  as  "changes"  instead 
of  "reactions." 


lProf.  G.  Tamman,  Sprechsaal  No.  35,  1904,  summarizing  his  studies  on  sili- 
cates says,  "The  volume  of  the  glass  is,  at  the  lowest  temperatures,  larger  than 
that  of  crystals."  Mellor,  Vol.  V,  p.  78,  discusses  the  volume  changes  in  silicates 
and  cites  A.  Laurent  (Ann.  Chim.  Phys.  (2)  66,96,1837;  A.  Brongniart,  Traite  des 
Arts  Ceramiques,  1,  283,  720,  1877)  and  G.  Rose  (Pogg,  111,  123,  1890;  A.  R.  Day 
and  E.  S.  Shephard,  Am.  Jour.  Science,  (4)  22,  262,  1906.  Dr.  E.  Berdel  (cited 
Vol.  VII,  p.  148  A.  C.  S.  Trans.)  described  similar  physical  changes  in  the  heat- 
ing of  ceramic  materials  and  bodies. 


PURDYj 


PYEO-PHYSICAL    AND    CHEMICAL    PROPERTIES. 


251 


The  greater  portion  of  the  constituents  of  our  clays  being  mineral 
substances,  many  of  which  do  not  entirely  lose  their  identity  in  the 
burning  of  clay  wares,  it  is  most  natural  that  these  should  exhibit  in 
nature  the  same  changes  when  treated  separately  that  they  do  when 
heated  together  in  clays..  Roth1  gives  the  following  description  of  in*1 
physical  changes  in  minerals  on  melting: 

Table  XXXVIII. 


Mineral. 

Specific 
Gravity  of 
the  Crystal. 

Specific  Grav- 
ity when 
melted  toglass 

Percent  Re- 
duction  in 
Spec.  Gravity. 

Remarks. 

Quartz 

2.663 
2.65 
3.3813 
3.0719 

2.561 
2.5522 

2.58 

2.574 

'2.5883 

2.5393 

2.604 

2.66 
2.6081 
2.6141 
2.7333 

3.2159 

3.2667 

3.409 

3.90 

3.838 

2.680 

2.751 

2.643 

2.576 

2.710 

2.667 

2.779 

3.100 

2.228 

2.19 

2.8571 

2.2405 

2.3512 

2.33551 

2.381 

2.328 
2.3073 
2.3069 
2.041 

2.258 
2.3621 
2.1765 
2.5673 

2.8256 

2.8035 

2.984 

3.05 

3.310 

2.427 

2.496 

2.478 

2.301 

2.43 

2.403 

2.608 

2  664 

16.3 
17.3 

15.6 
27.0 

8.1 

8.5 

7.6 

9.6 
10.9 

9.1 
21.9 

15.1 

9.1 
16.7 
6.1 

12.2 
14.2 
12.5 
20.5 
25.6 
12.9 

9.3 

6.2 
10.7 
10.3   ' 

9.8 

6.3 

14.2 

Quartz 

Olivine 

Average. 

Mica 

( j lass  compact. 

Glass  full  of  fine  bubbles. 

Adular 

Adular 

Glass  full  of  fine  bubbles. 

Sanidine 

Glass  full  of  fine  bubbles 

Orthoclase 

and  dark-colored. 
Glass  full  of  fine  bubbles. 

Orthoclase 

Glass  colorless. 

Microcline 

Glass  colorless. 

Albite  

Full  of  fine  bubbles;  white 

Oligoclase 

glass. 

White  glass;  bubbly. 

Labradorite 

Glass  slightly  bubbly,  with 

Hornblende 

black  and  white  portions 
Glass  compact. 

Augite 

Red  brown  garnet 

Lime-iron  garnet 

Granite 

Green  glass. 

Green  glass;  transparent; 

strongly  blebbed. 
Black    glass ;      opaque; 

strongly  blebbed. 
Black     glass ;     opaque; 

strongly  blebbed. 
Transparent;  veryblebby; 

difficult  of  fusion. 
Glass  homogeneous;  dark 

Hornblende  granite.. 

Felsite  porphyry 

Syenite 

Quartz  diorite 

Diorite,  quartz  free.. 

Gabbro 

colored. 

Glass  homogeneous;  dark 
colored. 

Black  glass;  opaque;  com- 
pact; somewhat  difficult 
to  fuse. 

Black  opaque  glass;  easily 

fusible. 

1  Not  in  original  table. 

The  alterations  in  the  minerals  and  rocks  above  cited  are  those  in- 
duced when  they  are  changed  by  melting,  from  a  crystalline  to  an 
amorphous  condition.  Such  complete  changes  as  this  cannot  be  per- 
mitted to  take  place  in  the  whole  mass  of  clay  ware  during  burning, 
and  yet,  as  will  be  shown,  the  percentage  of  decrease  in  specific  gravity 
of  many  of  our  clays  from  the  unburned  to  the  vitreous  stage  is  greater 
than  that  "given  in  the  above  data.  This  being  true,  it  is  evident  that 
there  are  factors  other  than  the  alteration  of  minerals  from  the  crystal- 
line to  the  amorphous  condition  that  affect  decrease  in  the  specific  grav- 
ity of  clays. 

In  the  following  table  are  given  data  which  show  the  effect  of  heat 
on  physical   structure  of  briquettes  made  from  various   clays: 

i  Allegemeine  unci   Chsmischa  Geologis,  Vol.   11,  p.   52. 


252 


PAVING    BEICK    AND    PAVING    BEICK   CLAYS. 


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PURDY  ] 


PYRO-PHYSICAL    AND    CHEMICAL    PROPERTIES. 


253 


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254  PAVING    BRICK   AND    PAVING   BRICK   CLAYS.  [bull.  no.  9 

It  was  a  surprise  to  learn  that  bricks  will  decrease  in  volume  with- 
out loss  of  weight,  and  at  the  same  time  decrease  in  specific  gravity. 
Had  the  clay  been  carried  to  complete  fusion,  i.  e.,  to  a  glass,  the  de- 
crease in  specific  gravity  would  have  been  credited  to  the  phenomenon 
as  in  the  case  of  minerals,  i.  e.,  the  changing  of  its  constituents  from 
crystalline  to  amorphous  forms.  But  in  the  case  of  a  clay  briquette,  a* 
small  portion  of  which  enters  into  the  fusion,  decreasing  in  specific 
gravity  before  the  minerals  have  been  rendered  amorphous,  i.  e.,  fused 
to  a  glass  or  even  before  vitrification  has  been  completed,  cannot  be 
explained  wholly  on  this  basis.  Mr.  C.  H.  Wegemann,  of  the  geological 
department,  was,  therefore,  requested  to  make  a  microscopic  study  of 
briquettes  of  two  different  clays  burned  at  different  temperatures.  His 
report  follows : 

Notes   ox   the  Microscopic   Structure  of  Certain  Paving  Brick  Clays,  at 

Various    Stages  of   Fusion. 

[By  C.  H.  Wegemann.] 

In  the  hope  of  explaining  some  of  the  phenomena  of  simultaneous  decrease 
in  volume,  porosity  and  specific  gravity  without  loss  in  weight  and  to  obtain 
some  idea  of  the  manner  in  which  fusion  takes  place  in  a  vitrifying  brick, 
microscopic  sections  were  prepared  from  briquettes  of  two  paving  brick 
clays. 

GENERAL    STRUCTURE. 

Thin  sections  of  the  briquettes  burned  at  a  low  temperature  exhibit  under 
the  microscope  a  very  fine-grained  fragmental  ground  mass,  or  matrix,  in 
which  are  imbedded  crystalline  and  other  fragments  which  were  present  in 
the  original  clay.  Prom  these  materials  are  developed,  at  high  temperature, 
amorphous  glasses  and  crystals. 

The  cavities  between  the  particles  of  a  brick  may  be  divided  into  two 
classes: 

(1)  Pores,  which  are  present  in  pieces  fired  at  low  temperatures,  due  to  the 
incomplete  consolidation  of  the  clay.  These  are  the  original  interstitial  spaces  of 
the  unburnt  clay. 

(2)  Blebs  or  bubbles,  which  are  formed  in  the  glass  at  higher  temperature  by 
the  liberation  and  expansion   of  gases. 

Pores  of  the  first  sort  are  of  small  size  and  irregular  outline.  As  the 
temperature  increases,  and  the  material  of  the  matrix  gradually  fuses  into 
glass,  these  interstitial  spaces  tend  to  disappear. 

Cavities  of  the  second  sort,  which  we  may  for  convenience  designate  as 
blebs,  are  simply  gas  bubbles  in  glass.  They  are  circular  in  outline  and 
vary  greatly  in  size.  They  are  not  present  in  the  bricks  burned  at  lower 
temperatures,  but  appear  only  after  the  formation  of  considerable  glass. 

DESCRIPTION   OF   SLIDES. 

R3-14 — This  briquette  was  drawn  at  cone  3  or  about  1190°C.  The  color  is 
red.  Under  the  microscope,  the  earthy  matrix  or  ground  mass  is  dark  brown, 
the  color  being  due  to  the  presence  of  iron  oxides. 

The  mineral  fragments  are  quartz,  feldspar  and  mica,  named  in  the  order 
of  their  abundance.  They  are  angular  in  outline,  the  thin  edges  being 
sharply  defined. 

Glass  has  formed  to  some  extent  throughout  the  ground  mass  and  in  a  few 
instances  it  has  separated  out  into  clear  transparent  masses,  in  several  of 
which  blebs  appear.  The  blebs,  however,  are  so  few  and  so  small  that  the 
cavities  may  be  considered  as  made  up  almost  entirely  of  pores  of  the  first 
class.     As  estimated  under  the  microscope,  the  porosity  is  1.9  per  cent. 


purdy]  PYRO-PHYSICAL    AND   CHEMICAL    PROPEETIES.  255 

R3-16 — Drawn  at  cone  5,  or  approximately  1230°C;  color  dark  brown. 
Under  the  microscope  the  ground  mass  appears  somewhat  denser  and  darker 
than  in  R  3-14.  The  quartz  fragments  are  apparently  unchanged.  The 
feldspar  fragments,  however,  have  disappeared.!  Mica  is  present,  but  in 
very  small  quantity. 

Glass  has  been  formed  in  considerable  amount.  It  appears  in  clear  trans- 
parent areas,  often  0.1mm.  in  diameter.  In  some  of  the  glass,  needle-like 
crystals  have  begun  to  form,  but  where  free  from  these  the  glass  is  color- 
less. This  fact  would  seem  to  indicate  that  but  little  iron  has  entered  into 
its  composition. 

As  stated  above,  fine  needle-like  crystals  are  often  present,  imbedded  in 
the  glass.  They  do  not  appear  to  have  any  definite  arrangement  with  re- 
spect to  each  other,  but  occur  singly  or  in  dense  masses.  When  viewed 
singly  they  are  colorless,  but  when  seen  in  masses,  they  possess  a  greenish 
yellow  tint,  which  they  impart  to  the  glass  in  which  they  are  imbedded. 
What  the  crystals  are  was  not  determined. 

The  iron  oxides  present  in  the  matrix  have  become  segregated  into  dense 
masses,  which,  where  they  transmit  light  at  all,  show  the  red  of  hematite, 
but  no  definite  crystals  are  to  be  seen.  Pores  of  the  first  class  have  dis- 
appeared, and  blebs  in  the  glass  have  become  numerous  and  large,  their 
average  diameter  being  0.066  mm.  The  estimated  pore  space  has  increased 
to  4.2  per  cent. 

R  3-18 — Drawn  at  cone  7,  or  1270°C.  The  fragments  of  quartz  appear  un- 
changed. The  earthy  ground  mass  is  rapidly  fusing  into  glass,  which  has 
increased  greatly  in  amount  over  that  in  the  preceding  slide.  The  fine  needle- 
like crystals  are  also  present  in  greater  number. 

Minute  crystals  of  iron  oxide  are  seen,  apparently  in  the  form  of  rhom- 
bohedrons,  having  slightly  concave  faces.  They  do  not  exceed  0.0014  mm. 
in  diameter.  The  blebs  have  an  average  diameter  of  0.1  mm.  and  the  pore 
space  has  increased  to  12.05. 

R  3-20 — Drawn  at  cone  9,  or  approximately  1310°C.  Quartz  fragments  are 
present  as  before,  but  occasionally  one  is  observed  the  edge  of  which  has 
fused  into  a  glass.  The  needle-like  crystals  are  everywhere  present  in  the 
glass,  giving  to  it  the  yellowish-green  tint  before  mentioned.  The  iron  ox- 
ides appear  much  the  same  as  in  the  last  specimen.  The  blebs  are  but  little 
changed. 

R  3-22 — Drawn  at  cone  11,  or  approximately  1350°C.  The  earthy  matrix 
has  given  place  entirely  to  glass.  Quartz  particles  are  still  present,  but  thin; 
their  edges  have  been  rounded  by  fusion. 

The  fine  needle-like  crystals,  in  the  glass  have  increased  greatly  in  length, 
being  in  some  cases  0.03  mm.  long.  They  exhibit  for  the  first  time  a  marked 
tendency  to  collect  in  radiating  clusters.  Often  they  appear  to  be  attached 
to  the  corners  of  the  crystals  of  iron  oxide.  These  latter  have  increased  in 
number  and  size,  being  0.005  mm.  in  diameter.  In  some  cases  the  individ- 
uals unite,  forming  long  serrated  columns. 

Blebs  have  increased  in  size,  their  average  diameter  being  0.128  mm. 
The  pore  space  as  estimated  from  them  is  19  per  cent. 

q  n-K) — Drawn   at   cone   02,  or  approximately  1110°C.     Color,   brick   red. 

As  in  the  R  3  series  already  described,  the  mineral  fragments  consist  of 
quartz,  feldspar  and  mica.  Very  little  glass  seems  to  have  developed  at  this 
temperature,  and  no  blebs  are  present.  The  pore  space  is  made  up  entirely 
of  pores  of  the  first  class,  or  those  due  to  the  imperfect  consolidation  of 
the  bricks.  The  average  diameter  of  these  pores  is  0.065  mm.,  and  the  pore 
space  as  calculated  is  2.6  per  cent. 


l  Hintze  gives  the  fusion  points  of  the  feldspar  as  ranging  from  1140C,  in 
sanicline  to  1230  C,  in  labradorite.  In  the  briquette  under  consideration  it  is 
evident  that  the  feldspar  has  fused  into  glass.  It  is  to  be  supposed  that  in  this 
fusing,  it  would  flux  some  of  the  quartz.  If  it  did  so,  however,  the  quartz  must 
have  been  furnished  by  the  ground  mass,  for  the  coarser  fragments  are  apparently 
not  changed  in  outline  nor  diminished   in  amount. 


25P)  PAVING    BRICK    AND    PAVING    BRICK   CLAYS.  [bull.  no.  9 

G  11-12 — Drawn  at  cone  1,  or  approximately  1150°C.     Color  red. 

A  little  glass  appears,  but  no  blebs  are  seen.  The  average  size  of  pores 
is  lower  than  in  the  last  slide,  being  0.045,  but  the  pore  space  as  estimated 
runs  a  little  higher,  or  3.6  per  cent. 

It  may  be  remarked  that  in  the  slides  there  is  no  marked  increase  in 
the  pore  space,  as  temperature  increases,  up  to  the  point  where  blebs  appear. 
From  that  point  on,  pore  space  increases  rapidly. 

G  11-14 — Drawn  at  cone  3,  or  approximately  1190°C.     Color,  reddish  brown. 

Fine  needle-like  crystals  have  formed  in  the  glass.  A  few  blebs  appear, 
but  are  not  in  sufficient  number  to  affect  the  pore  space  materially.  As 
estimated,  is  is  3.2  per  cent,  while  the  average  size  of  the  pores  of  both  classes 
is  0.06  mm. 

G  11-15 — Drawn  at  cone  5,  or  approximately  1230°C.     Color,  dark  brown. 

Quartz  fragments  are  still  present,  but  the  feldspar  and  mica  have  dis- 
appeared. Glass  has  formed  in  great  quantity,  being  colorless,  or  when 
acicular  crystals  are  present,  greenish  yellow.  These  crystals  are  present  in 
great  numbers  and  resemble  those  described  in  the  former  series.  Microlites 
of  iron  oxide  are  also  present,  but  have  not  yet  grouped  themselves  in  den- 
dritic forms.  Pores  other  than  blebs  have  disappeared,  but  the  blebs  have 
increased  greatly  in  size,  the  average  diameter  being  0.175  mm.,  while  the 
pore  space  amounts  to  12  per  cent. 

Summary  of  Changes  Observed  at  Different  Heat  Treatments. 

Cone   12 — Quartz  and   feldspar  fragments  are  unchanged. 

But  little  glass  is  developed. 

No  blebs  have   yet  formed. 
Cone     1 — No  marked  change  has  taken  place  over  cone  12. 
Cone     3 — A  small  amount  of  glass  is  developed  from  the  ground  mass. 

A  few  blebs  appear. 

Needle-like   crystals   are   developed  in  the   glass. 
Cone     5 — Feldspar   fragments   are   fused   into   glass. 

Quartz   fragments  are   fused   into   glass. 

Blebs  increase  in  number  and  size. 
Minute   crystals  of  iron  oxide   develop. 
Cone     7 — ©lass  increases  in  amount. 

Blebs  increase  in  number  and  size.  t 

Quartz  fragments  are  unchanged. 
Cone     9 — Quartz  fragments  begin  to  fuse  into  glass  along  their  edges. 
Cone  11 — Ground  mass  is  completely  fused  into  glass. 

Some   rounded  quartz   fragments   still   remain. 

Blebs   have   increased  remarkably  in  size   and  number. 

Microlites  are  more  numerous. 
It  should  be  borne  in  mind  that  this  is  but  a  preliminary  study.    The  num- 
ber of  slides  examined  is  too  limited  to  warrant  broad  generalizations. 

Specific  Gravity,  Volume  and  Porosity  Changes  of  Clays  Studied. 

(by  r.  c.  purdy.) 

Owing  to  the  absence  of  similar  data  on  other  clay  samples  and  the 
incompleteness  of  the  present  researches,  the  writer  has  no  definite  con- 
clusions to  present  concerning  the  surprising  facts  presented  by  Mr. 
Wegemann.  This  data  does,  however,  establish  the  facts  that  neither 
a  mineralogical  analysis  nor  an  ultimate  or  rational  analysis  of  clay 
will  indicate  the  nature  of  its  pyro-chemical  and  physical  behavior. 
Indeed,  the  above  data  would  seem  to  throw  doubt  on  the  value  of  pyro- 
chemical  and  physical  study  of  a  synthetic  mixture  of  minerals  as  a 
basis  on  which  to  interpret  the  thermal  changes  in  an  "unknown"  clay 
mixture. 

In  the  following  figures  26  and  27  are  shown  the  specific  gravity, 
volume  and  changes  in  porosity  in  the  two  clays  of  which  microscopic 
studies  were  made  by  Mr.  Wegemann.     It  will  be  seen  that  all  three 


PURDYj 


PYKO-PHYSICAL    AND   CHEMICAL    PROPERTIES. 


257 


factors  decrease  simultaneously,  showing  that  the  increases  in  molecular 
volume  and  in  bleb  structure  is  not  sufficient  to  counteract  the  shrink- 
age of  the  mass  as  a  whole,  and  is  not  to  be  accounted  for  by  the  sealing 
up  of  the  original  pores. 


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PAVING   BRICK   AND    PAVING   BRICK-  CLAYS. 


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purdy]  PYRO-  PHYSICAL    AND   CHEMICAL    PROPERTIES.  259 

Differentiation  Between  Clays  on  Basis  of  Difference  in  Rate 
.  and  Manner  of  Decrease  in  Porosity  and  Specific  Gravity. 

introduction. 

Importance  of  Slow  Vitrification* — It  is  the  concensus  of  opinion 
among  those  who  have  given  serious  thought  to  the  vitrifying  proper- 
ties of  ceramic  mixtures,  whether  natural,  as  ordinary  clay,  or  artificial, 
as  pottery  bodies,  that  those  mixtures  which  vitrify  most  slowly  and  at 
a  uniform  rate,  all  other  things  being  usual,  will  produce  the  strongest 
and  toughest  ware.  Chemical  analysis  and  synthetical  mixtures  have 
failed  to  reveal  the  happy  combination  of  minerals  or  chemical  ele- 
ments that  will  produce  this  slow,  uniform  rate  of  vitrification.  A  few 
general  rules  can  be  stated  as  to  combinations  of  ingredients  required 
to  produce  tough  bodies,  but  none  of  them  can  be  applied  with  absolute 
assurance  that  they  will  operate  in  a  given  case.  With  our  present  in- 
formation empirical  trials. have  to  be  resorted  to  find  the  proper  com- 
bination in  each  case. 

It  is  commercially  impractical  to  alter  the  composition  of  clays  used 
for  paving  brick  manufacture  except  in  so  far  as  different  strata  permit 
of  the  use  or  rejection  of  materials  that  effect  the  character  of  the  ware. 
This  the  paving  brick  manufacture  has  learned  by  experience,  so  that 
the  composite  "dry  pan"  sample,  before  described,  is  supposed  to  repre- 
sent the  best  "mix"  that  is  commericially  possible  in  a  given  case.  On 
the  supposition  that,  according  as  its  rate  of  vitrification  is  slower,  one 
clay  is  more  suited  for  vitrified  paving  brick  than  another,  and  that 
there  is  no  means  of  obtaining  information  that  bears  on  this  problem 
other  than  determining  this  very  pyro-physical  property  in  paving  brick 
clays,  clays  were  molded  into  cones  having  the  same  shape  and  dimen- 
sions of  Seger  pyrometric  cones  manufactured  by  Prof.  Edward  Orton, 
Jr. 

PRELIMINARY  TRIALS. 

Manufacture  of  Test  Cones — The  clays  in  this  experiment  were  dry 
ground  in  a  mortar  to  pass  a  40  mesh  screen,  wetted  with  water  from 
the  University  mains,  wedged  thoroughly  and  molded  into  cones  with 
a  spatula  in  a  regular  cone  die  as  used  by  Orton.  On  the  upper  face  of 
each  cone  was  scratched  its  sample  and  serial  number.  After  removal 
from  the  die  the  cones  were  placed  in  a  cool  place  protected  from  drafts 
to  dry. 

Setting  of  Test  Pieces  After  Drying — One  cone  each  of  four  different 
clays  was  set  in  a  row  in  the  center  of  a  fire  clay  slab.  On  either  side 
of  the  row  of  test  cones  was  placed  a  row  of  three  standard  Seger  cones 
arranged  in  opposite  order  from  one  another.  There  were  eight  groups 
of  such  slabs  for  each  set  of  four  test  cones,  thus  allowing  eight  heat 
treatments  of  different  intensities  on  each  clay. 


260  PAVING   BKICK   AND    PAVING   BRICK   CLAYS.  [bull.  no.  9 

The  eight  groups  with  the  standard  cones  were  as  follows : 

First  group  010-09-08. 
Second  group  07-06-05. 
Third  group  04-03-02-01. 
Fourth  group  01-1-2. 
Fifth  group  2-3-4. 
Sixth  group  4-5-6. 
Seventh  group  6-7-8. 
Eighth  group  8-9-10. 

Special  saggars  were  prepared,  being  3y2  inches  deep  and  8  by  8 
inches  in  area,  and  having  only  three  sides.  These  saggars  were  placed 
in  four  bungs  in  the  side  down-draft  kiln  designed  by  the  writer  for  the 
ceramic  department  of  the  University  of  Illinois,  and  shown  in  Fig.  28. 
Four  of  these  special  saggars  were  placed  in  each  bung,  making  16  sag- 
gars in  all. 

Burning — Four  separate  burns  were  made,  one  of  the  first  four 
groups,  one  of  the  last  four  groups,  and  a  duplicate  or  check  burn  on 
each. 

The  kiln  was  fired  with  coke,  in  a  manner  that  maintained  oxidizing 
conditions  throughout  the  entire  burn.  In  all  four  burns  the  fire  clay 
slabs  were  burned  to  a  clean  buff  color  showing  no  evidence  of  having 
been  subjected  at  any  time  to  reducing  influence's.  Inasmuch  as  the  buff 
color  of  a  fire  clay  is  very  sensitive  to  reducing  action,  and  if  once  re- 
duced the  buff  tint  is  irrevocably  bleached,  confidence  is  felt  that  in 
these  burns  we  were  successful  in  maintaining  oxidizing  conditions. 

When  a  temperature  had  been  reached  sufficient  to  cause  cone  09  to 
bend,  the  wicket  was  opened  and  the  top  saggers  from  each  of  the  four 
bungs  were  drawn  and  placed  in  the  ash  pit  of  the  kiln  where  they 
cooled  slowly.  After  placing  a  cover  over  the  exposed  cones  left  in  the 
kiln,  the  wicket  was  resealed  and  the  heat  raised  until  cone  06  was  bend- 
ing, and  so  on  until  the  center  standard  cones  of  the  last  set  of  four  sag- 
gers were  bending. 

By  this  scheme  of  setting  twenty-four  clays  could  be  tested  in  one 
series  of  four  burns,  there  being  in  each  draw  two  slabs  of  the  same 
group  in  each  of  the  four  saggars.  This  scheme  of  burning  was  made 
possible  by  the  fact  that  the  openings  in  the  flash  wall  leading  into  the 
firing  chamber,  and  openings  in  the  opposite  side  of  the  firing  chamber 
leading  into  the  draft  flue  caused,  with  the  down  draft,  an  equal  lateral 
distribution  of  heat.  In  no  instance  was  there  a  failure  to  have  the 
center  test  cone  bent,  although  in  some  cases  in  the  same  draw  it  was 
bent  more  than  in  others. 

Testing  of  the  Trial  Pieces — The  cones  were  detached  from  the  slabs, 
marked  with  lead  pencil,  weighed  one  at  a  time  on  a  jolly  balance  and 
then  placed  in  clear  hydrant  water.  After  twenty-four  hours  of  satura- 
tion, the  wet  and  immersed  weights  of  each  cone  were  made  and  from 
the  data  so  obtained,  their  porosity  and  apparently  specific  gravity  cal- 
culated. 

Difficulties  Encountered — First,  when  the  cones  were  detached  from 
the  slabs  many  broke  into  two  or  more  pieces;  second,  a  few  of  the  cones 
were  bloated  at  the  base,  due  to  a  lack  of  oxidation  ;  third,  the  cones  were 


PURDY] 


PYRO-PHYSICAL    AND    CHEMICAL    PROPERTIES. 


261 


\h  l 


E 


Ah 


*■. 


Lk^-O- 


S.B 


i: 


>  H 
h 

£<  i 

z 


invariably  vitrified  more  at  the  top  than  at  the  base,  thus  causing  ir- 
regularity of  results  in  those  that  were  broken;  fourth,  in  those  cones 
which  had  softened  sufficiently  to  cause  them  to  bend  over,  the  pore  sys- 
tem was  not  normal,  owing  to  the  strain  set  up  on  the  upper  side  and 
compression  on  the  under  side  of  the  bent  cone;  fifth,  we  were  not  sue- 


262 


PAVING    BRICK   AND    PAVING    BRICK    CLAYS. 


[BULL.    NO.    9 


cessful  in  making  a  jolly  balance  spring  that  was  heavy  enough  to  pre- 
vent the  weight  of  a  cone  stretching  it  beyond  its  elastic  limit,  give  suffi- 
ciently delicate  reading. 

Data  Obtained — 'Although  the  test  as  a  whole  was  unsatisfactory,  it 
is  believed  that  the  data  obtained  has  a  value.  The  porosity  data  were 
ploted  on  a  diagram  as  shown  in  Figure  29.  In  this  the  linear  distance 
between  points  on  the  abscissa,  indicating  difference  in  melting  periods 
of  the  standard  cones,  is  equal  to  the  linear  distance  assigned  to  repre- 
sent a  difference  of  two  per  cent  in  porosity.      The  solid  line  is  drawn 


40 

v 

\ 
\ 

\ 

\ 

>s> 

\ 

i 

5  15 
10 

\ 

& 

\ 

V 

5 

\ 

V 
V 

0 

09 

06 

ol 

TEMPERATURES  IN  TERMS  OF  COXES 
Fig.  29.     Decrease  in  porosity  with  burning  in  terms  of  cones. 

through  points  representing  the  average  data  obtained  on  the  two  dup- 
licate cones,  and  the  points  indicated  but  not  on  the  heavy  black  line 
represents  in  each  case  the  data  obtained  from  each  of  the  two^  cones. 
In  case  the  data  for  one  of  the  duplicate  cones  were  missing,  as  in  K  2 
for  instance,  the  heavy  black  line  traces  the  points  representing  the  de- 
termined data. 


PURDYj 


PYRO-PHYSICAL    AND   CHEMICAL    PROPERTIES. 


263 


The  dotted  line  was  drawn  through  all  possible  combinations  of  three 
points  that  were  found  to  lie  in  line  with  each  other.  In  some  cases 
there  was  only  one  light  line  and  in  others  more  than  one,  as  shown 
by  the  data  given  in  Table  XL,  The  lines  drawn  through  three  points 
lying  in  a  straight  line  are  taken  as  representing  the  slope  of  the  curve 

s  ribing  the  change  in  porosity  with  regularly  increasing  intensity 
of  heat  treatment.  Where  there  is  a  possibility  of  more  than  one  slope, 
as  indicated  by  the  light  lines,  each  is  recorded  and  their  average  cal- 
culated. The  data  in  Table  XXX  is,  therefore,  the  slope  or  tangent  of 
the  angle  that  the  light  lines  drawn  through  three  points  makes  with  the 
abscissa. 

To  obtain  this  data  a  protector  was  so  placed  on  the  line  that  the 
angle  could  be  read.  The  natural  tangent  of  the  angle  was  then  ob- 
tained from  a  logarithmic  table  of  natural  functions.  Since  the  tangent 
of  the  angle  which  a  line  makes  with  a  given  base  line,  is  the  slope  or 
inclination  of  that  line,  this  tangency  can  be  taken  as  representing  the 
rate  at  which  the  porosity  decreases  with  increasing  heat  treatment. 

In  the  following  Table  will  be  found  the  values;  first,  of  each  of  the 
tangents  of  the  angles  made  by  the  dotted  line  and  abscissa;  second,  the 
average  of  the  tangents;  and  third,  the  rattler  loss  as  determined  on 
bricks  obtained  from  factories  using  the  several  clays. 

Table  XL. 


Rate  of  Vitrification. 

Sample. 

1 

2 

3 

4 

Average. 

Rattler  Loss. 

K      1 

1.1708 
1.9007 
2.0323 
1.9626 
2.0732 
2.0503 
1.5900 
1.4733 
2.0965 
1.5301 
1.1041 
1.0538 
1.0265 
1.0355 
1.5697 
1.3270 
0.6208 
0.9601 
1.0538 
.9657 
1.9347 
1.2799 
2.5386 
2.4142 
1.1041 
1.1106 
2.7475 
2.5826 

1.1708 
1.9007 
2.0323 
1.9626 
2.0732 
2.0503 
1.7870 
1.6204 
1.5208 
1.5301 
1.3079 
1.3322 
0.9986 
1,3714 
1.5783 
1.3270 
0.6669 
1.1677 
1.2799 
1.5470 
1.7558 
1.2799 
2.5386 
1.9391 
1.6325 
1.2344 
2.7475 
2.5826 

15.82 

K      2 

17.48 

K      3 

24.89 

K-  4 

K      5 

19.77 

19.36 

K—  6 

13.25 

K—  7 

1.9810 
1.7675 
1.1504 

13.89 

K—  8                              

20.03 

K—  9    .                 

1.3151 

14.84 

K— 10 

35.74 

K— 11 

1.1508 
1.6107 
0.9708 
1.2685 
1.9486 

28.13 

K— 12 

K    13 

31.50 

K— 14 

1.8103 
1.2167 

21.24 

S  —  1 

26.25 

S  —  2 

27.94 

R—  1 

0.7673 
1.7321 
1.5061 
2.1283 
2.1445 

0.6128 
0.8541 

16.92 

R—  2 

1.1237 

17.80 

R—  3    . 

14.80 

R—  4 

15.33 

H     16 

1.1882 

H    18 

H    20 

H    21 

1.4641 
2.1609 
0.7954 

H—  1 

29.61 

H    24 

0.6208 

H    23 

B—  1 

28.03 

Summary — Owing  to  the  unavoidable  inaccuracies  of  the  work  and  the 
erroneous  assumption  that  a  porosity  graph  would  trace  a  straight  line, 
the  data  given  in  the  above  Table  has  but  little  value.  Its  principal  value 
lies  in  the  developed  fact  that  as  a  rule  the  slower  the  clay  fuses  the 
tougher  appears  to  be  the  mass. 


264 


PAVING   BRICK   AND    PAVING    BRICK   CLAYS. 


[BULL.   NO.    9 


FINAL  TRIALS. 

Failing  to  solve  the  problem  at  hand  in  the  above  test,  another  and 
more  thorough  investigation  was  at  once  started,  using  not  only  a  large 
number,  but  also  a  larger  variety  of  clays.  The  manner  in  which  the 
test  pieces  for  this  latter  study  were  prepared  was  as  follows: 

Wedging — Approximately  one  pound  of  dry  clay  was  placed  on  a 
dampened  plaster-covered  table  and  sufficient  water  from  the  University 
mains  added  to  develop  the  plasticity  required  to  permit  batting  the  clay 
into  loaves.  This  was  accomplished  by  adding  water  in  small  quantities, 
and  thoroughly  working  it  into  the  clay  each  time,  until  the  mass  had  the 
desired  plasticity.  It  was  then  thoroughly  wedged  by  kneading  and 
batting  until,  on  cutting  the  mass  open,  it  appeared  to  be  compact,  i.  e. 
without  air  blebs. 

Molding — The  loaf  was  then  subdivided  into  smaller  portions,  each 
just  sufficient  to  fill  a  mold  %  inch  by  21/4  by  4%  inches.  The  slabs 
were  made  to  fill  the  mold  by  pressure  applied  in  a  screw  press.  They 
were  then  placed  in  a  miter-box  and  cut  into  briquettes  %  inches*  by  1% 
inch  by  2%  inches. 

Marking — The  laboratory  sample  number  and  a  serial  number  was 
stamped  on  each  briquette. 

Drying — The  briquettes  were  dried  in  an  open  room  at  summer  heat. 
It  had  been  found  possible  to  dry.  even  the  most  tender  of  clays  in  this 
manner,  so  it  was  assumed  that  all  clays  used  in  this  test  could,  with- 
out detriment,  be  subjected  to  this  treatment. 

Firing — Twenty-four  briquettes  of  each  clay  were  prepared.  The  ones 
on  which  the  serial  numbers  1  and  2  had  been  stamped  were  placed  in 
a  saggar  to  be  drawn  at  cone  010,  those  on  which  the  serial  numbers  3 
and  4  were  stamped  were  placed  in  a  saggar  to  be  drawn  at  cone  08 
and  so  on — each  successive  pair  of  briquettes  of  each  clay  being  placed 
in  a  saggar  to  be  drawn  at  a  predetermined  heat  treatment  as  follows: 


Series  No.  on  briquette. 

Heat  at  which 
drawn. 

Hours  interven- 
ing between 
draws. 

1,2.                                

010 

08 

06 

04 

02 

1 

3 

5 

7 

9 

11 

Oxidized  at  800° 

3,4.                

for  2  hours. 

From  800° C  to 

cone  010  6  hours. 

2  hours 

5,6.                    : 

2  hours 

7,8 

2  hours 

9  10  .                                                  

2  hours 

11, 12. .  . .            

2  hours 

13,14..     .            

2  hours 

15,16 

2  hours 

17,18.   ..                  

2  hours 

19, 20.                        

2  hours 

21,22.                                       

2  hours 

PURDY]  PYRO-PHYSICAL    AND   CHEMICAL    PROPERTIES.  265 

The  briquettes  in  the  saggars  to  be  fired  from  cones  3  to  11  were 
parked  loosely  in  coarse  white  placing-sand,  as  to  prevent  their  stick- 
ing Dne  to  another.  Only  those  clays  known  to  be  fire  clays,  or  at 
least  sufficiently  refractory  to  withstand  severe  heat  treatment  were 
placed  in  the  saggars  to  be  drawn  at  the  higher  cones. 

The  eleven  saggars  were  placed  in  a  coke-fired,  side  down-draft  kiln 
in  a  manner  convenient  for  drawing.  The  "spy"  cones  were  centrally 
located  in  the  kiln  in  a  shield  that  protected  them  at  all  times  from 
direct  contact  with  the  flame.  When  cone  010  was  bent  over  sufficiently 
to  touch  the  plaque,  the  wicket  was  opened  enough  to  draw  the  cone 
010  saggar,  the  wicket  replaced,  and  the  heat  slowly  raised  as  shown 
in  the  above  table. 

Cooling— The  saggars  in  which  the  briquettes  were  placed  were  "tile 
setters"  2  inches  deep  and  8  inches  by  8  inches  in  area.  Before  plac- 
ing, another  saggar  was  inverted  over  the  one  containing  the  briquettes, 
so'that  on  drawing,  the  briquettes  were  at  no  time  exposed  to  the  rela- 
tively cold  temperature  of  the  room,  except  in  one  case  of  accident. 
The  saggars  were  placed,  uncovered,  in  the  ash  pit  of  the  kiln,  where 
they  were  exposed  to  the  direct  radiation  from  the  hot  grate  bars  above. 
In  this  manenr,  the  briquettes  were  cooled  rapidly  at  first,  thus  pre- 
venting the  fused  portions  in  the  briquettes  from  crystallizing  very 
much,  but  from  dull  redness  down  to  blackness  the  cooling  extended  over 
a  considerable  period. 

The  method  of  cooling  pursued  in  this  investigation  was  not  ideal. 
The  briquettes  should  have  been  cooled  slowly  for  the  first  200°  C. 
which,  as  above  stated,  was  not  the  case.  Inasmuch  as  there  is  danger 
of  checking  the  vitrified  briquettes  by  cooling  down  to  room  temper- 
ature too  rapidly,  some  attention  should  be  given  to  the  last  as  well  as 
to  the  first  stage  of  the  cooling  period,  but  more  particularly  to  the 
first.  It  was  not  possible  to  cool  the  briquettes  under  these  ideal  con- 
ditions, for  the  services  of  the  kiln  were  in  demand  for  other  purposes, 
and  circumstances  did  not  permit  of  delaying  the  burning  until  such 
time  as  the  kiln  would  not  be  in  use. 

Preparation  of  Briquettes  for  Testing — When  cooled,  sand  grains  were 
found  to  be  fused  to  many  of  the  briquettes,  requiring  that  they  be 
ground  off  on  an  emery  wheel.  Care  was  taken  not  to  unduly  heat  the 
bricks  while  grinding  off  the  sand,  and  yet  as  little  water  as  possible 
was  used.  The  bricks  that  were  thus  ground  were  washed  in  distilled 
water  to  remove  all  traces  of  dirt,  and  adhering  particles.  From  the 
unground  briquettes  all  adhering  particles  wrere  removed  by  a  dry  stiff 
brush.  Each  briquette  was  carefully  examined  for  flaws  induced  during 
manufacture  or  cooling,  and  also  in  order  to  remove  all  adhering  por- 
tions, such  as  broken  corners  that  might  have  been  detached  later  in 
the  test. 

Up  to  this  point,  all  briquettes  were  handled  together,  without  re- 
gard to  sample  or  series  number,  except  as  before  indicated. 


266 


PAVING    BRICK    AND    PAVING    BRICK   CLAYS. 


[BULL.   NO.    9 


In  all,  60  clays  were  prepared  for  testing,  as  above  described,  using 
16  to  22  briquettes  for  each.  The  briquettes  were  not  sorted,  those 
of  each  clay  being  treated  as  a  unit,  so  as  to  insure  like  conditions  at  all 
times  for  all  briquettes  of  the  same  clay. 

.  Drying  of  Briquettes — Briquettes  belonging  to  two  or  three  clays 
were  placed  m  a  drying  oven  and  dried  at  240°  C.  At  the  expiration 
of  four  hours  at  this  temperature,  they  were  cooled  in  .dessicators  pre- 
paratory to  obtaining  the  dry  weight  of  each  briquette.  The  dry  weight 
of  each  briquette  was  found  to  the  third  decimal  place  on  a  chemical 
balance. 

Sal /nation  of  Briquettes — After  the  dry  weights  had  been  obtained, 
the  briquettes  were  placed  in  aluminum  pans,  keeping  them  arranged  in 
the  pans  in  their  regular  serial  order.  Distilled  water  was  added  until 
only  the  upper  surface  of  each  test  piece  was  above  the  level  of  the 
water.  This  exposure  of  one  face  of  the  briquette  was  to  permit  easy 
escape  of  the  air  from  the  interior  of  the  brick,  as  it  was  being  displaced 
by  the  distilled  water.  After  standing  thus  in  water  for  18  to  24 
hours,  they  were  completely  immersed. 

After  a  total  of  48  hours  in  water,  the  briquettes  were  placed  in 
water  under  a  bell  jar,  and  the  air  exhausted.  In  nearly  every  case, 
when  a  partial  vacuum  had  been  created,  the  air  escaped  from  the 
briquettes  at  such  a  rate  and  in  such  volumes  as  to  cause  the  water  to  ap- 
pear to  be  boiling.  From  a  previous  experiment,  the  data  of  which 
are  given  in  the  following  table,  it  was  thought  that  in  the  average 
case,  fairly  complete  saturation  could  be  attained  with  15  minutes  treat- 
ment in  a  partial  vacuum. 

Table  XLI. 

Showing  efficiency  of  vacum  treatment  in  effecting-  saturation. 


Sample. 

Porosity  as  de- 
termined after  48 
hours'  saturation 

without  air  ex- 
haustion. 

Percentage  of  Gain  in 
sity  at  Conclusion  of 
Treatment  extending 
period  of 

PORO- 
Vacuum 

OVER 

5  min. 

10  min. 

15  min. 

20  min. 

S—  2 

3.22 
3.3 
3.93 
4.22 
4.27 
4.51 
5.12 
5.29 
6.1 
6.46 
6.55 
6.7 
6.91 
7.53 
8.64 
9  06 
9.39 
19.8 

48.1 
38.7 
27.3 
13.48 
44.60 
33.40 
58.2. 
31.2 
27.5 
29.9 
18.6 
10.2 
28.0 
11.8 
11.8 
22.0 
13.11 
6.05 

51.8 
42.1 

57.9 
48.4 
35.6 
18.7 
46.6 
36.8 
61.7 
37.6 
35.6 
35.3 
21.6 
11.0 
31.4 
15.7 
14.1 
24.0 
23.4 
6.84 

65.0 

G-ll 

50.6 

K—  4b . 

37.5 

K-15d 

K— I3c 

14.48 
46. 1)0 
37.50 
59.4 
35.4 
32.2 
31.6 
20.1 
11.0 
30.4 
13.7 
12.8 
23.5 
20.3 
6.22 

20.8 
46.6 

K— 15c.             

38.2 

R—  4     

63.7 

H— 11 

38.9 

R—  2 

36.0 

K—  6d 

39.3 

K—  2 

24.3 

R—  1    .                   

11.0 

B  — 11          

32.0 

J  —  11 

16.0 

I  —  11   

14.8 

K—  8d.                     

24.9 

B—  1 

K— 15b 

7.34 

PURDY]  PTRO-PHYSIOAL    AND   CHEMICAL    PROPERTIES.  267 

Each  saturated  briquette  was  in  turn  suspended  by  a  silk  thread  from 
the  beam  of  a  chemical  balance,  and  its  saturated  weight  taken,  allowing 
for  the  weight  of  the  thread.  Without  removal  from  the  balance,  a  glass 
of  water  was  placed  on  a  bridge  spanning  the  scale  pan  in  such  a  man- 
ner as  to  cause  the  briquette  to  swing  absolutely  free  but  completely 
immersed  in  the  water.  The  suspended  weight  of  the  briquette  was 
thus  taken. 

Calculations — The  percentage  of  porosity  of  each  briquette  was  cal- 
culated by  the  formula : 

Wet  Weight  — Dry  Weight 

Percentage    of    Porosity  == -. X  100 

Wet  Weight  —  Suspended  Weight 

Plotting  of  Results — In  the  previous  study,  that  with  clays  molded 
into  cones,  the  writer  had  arbitrarily  established  the  following  propor- 
tion :  Linear  length  on  ordinate,  equal  to  2  per  cent  porosity ;  linear 
length  on  abscissa  equal  to  difference  of  heat  treatment  of  one  cone:  that 
is,  2:1.  This(  as  before  explained,  was  maintained  between  the  coordin- 
ate factors  of  the  porosity-graphs,  so  that  the  rate  of  decrease  in  porosity 
could  be  expressed  numerically  in  terms  of  the  tangency  or  slope  of 
the  curves,  and  that  the  factors  so  obtained  would  be  comparable  one 
with  another  at  all  times. 

The  divisions  on  the  abscissas  of  the  specific  gravity  curves  are  the 
same  as  those  of  the  porosity  curves.  The  divisions  on  the  ordinate  are 
proportionally;  0.1  Sp.  Gr.    :2  cone  heat   :  :1 :2. 

Data  obtained — In  the  following  table  are  the  data  obtained  in  the 
above  study.  Data  for  a  few  more  clays  were  obtained,  but  owing  to 
their  incompleteness  they  are  not  recorded  at  this  place : 


268 


PAVING    BRICK   AND    PAVING    BRICK   CLAYS. 


[BULL.   NO.    9 


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PURDY] 


PYRO-PHYSICAL    AND    CHEMICAL    PROPERTIES. 


269 


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270  PAVING   BRICK    AND    PAVING    BRICK   CLAYS.  [bull.  no.  9 

On  plotting  the  data  obtained  in  this  experiment  they  were  found  in 
most  cases  to  be  consistent,  i.  e.,  clay  used  for  particular  industries 
such  as  paving  brick,  fire  brick,  etc.,  exhibited  porosity  changes  that 
were  so  concordant  that  the  possible  commercial  use  for  each  was  pre- 
dicted from  the  curves  and  in  no  case  where  the  clays  are  now  being 
employed  did  the  predicted  use  differ  from  their  present  use  as  re- 
ported by  those  who  collected  the  samples. 

The  curves  in  every  instance  were  not  straight,  but  curved  so  that 
their  tangent  or  rate  of  declination  could  not  be  ascertained  without 
the  use  of  calculus.  Inasmuch  as  the  curves  did  not  describe  grad- 
ually sloping  curves,  but  in  most  cases  exhibited  well  defined  lags  in 
decrease  of  porosity,  it  was  found  that  a  simple  tangent  factor  would 
not  describe  in  full  the  fusion  behavior  of  the  clays.  A  complicated 
modulus  was  devised  which  was  not  only  a  function  of  the  tangents  of 
the  sections  of  the  curves  between  points  of  lag,  .but  also  the  length  of 
each  section.  Considering  the  fact,  however,  that  this  scheme  of  study- 
ing the  fusion  phenomenon  is  here  first  presented,  thus  not  finding 
confirmation  by  other  experimenters,  and  since  the  modulus  does  not 
show  more  clearly  the  rate  fusion  than  does  the  curve,  no  attempt  was 
made  to  apply  the  modulus  on  the  different  types  of  clays. 

SUMMARY   OF    RESULTS    OF   TESTS. 

In  subsequent  curves  are  given  the  limits  of  the  areas  traversed  by 
the  porosity  and  specific  gravity  curves  of  the  different  types1  of  clays. 

In  Fig.  30  are  shown  the  limits  of  area  traversed  by  porosity-graphs 
of  the  fire  clays.  The  fire  clays  are  grouped  into  three  classes  according 
to  their  rate  of  decrease  in  porosity. 

Number  One  Fire  Clays — The  writers  of  Clay  Eeports  have  heretofore 
failed  to  recognize  that  of  two  clays  having  similar  ultimate  chemical 
compositions  and  similar  ultimate  fusion  periods,  one  can  be  used  in 
No.  1  fire  brick,  while  the  other  would  fail  as  a  first-class  fire  brick 
material,2  and  the  one  failing  as  a  fire  brick  material  would  be  the  only 
one  that  could  with  success  be  used  in  the  stoneware  industry.  Sev- 
eral examples"  of  the  foregoing  were  noted  in  the  examination  of  the 
Illinois  fire  clays.     In  fact,  the  case  is  not  an  uncommon  one. 

In  fire  brick,  maintenance  of  an  open  structure  through  the  entire 
heat  range  used  in  the  various  ceramic  industries  is  essential.  On  the 
other  hand,  in  stoneware,  closeness  of  structure  at  comparatively  low 
temperatures,  or  early  vitrification  followed  by  a  long  fusion  range  is 
absolutely  required.  It  is  evident,  therefore,  that  a  classification  of  re- 
fractory fire  clays  (so  called  because  they  withstand  heat  equivalent 
to  cone  27  or  more  without  failure)   should  take  account  of  this  dif- 

1.  "Types,"  as  here  used,  does  not  refer  to  geological  origin  or  age,  but  rather 
to  the  possible  commercial  use  of  the  clays. 

2  By  fire  brick  material  is  meant  what  is  known  in  trade  as  No.  1  Are  brick 
The  so-called  No.  2  fire  bricks  are,  as  a  rule,  not  worthy  of  the  distinctive  title 
"fire  brick."  Used  in  places  exposed  to  fire  does  not  necessarily  make  a  brick  a 
fire  brick,  for,  if  this  were  so,  the  comparatively  fusible  Chicago  brick  placed 
in  the  arches  of  their  scove  kilns  would  have  to  be  called  "fire  brick." 


PURDY] 


PYRO-PHYSICAL    ANI>    CHEMICAL    PROPERTIES. 


271 


"W    TEMPERATURES  EXPRESSED  IN  CONES 

Fig.   30.     Differentiation  of  fire  clays  on  basis  of  porosity  changes. 

ference  in  their  manner  of  fusion.  This  essential  difference  in  the  be- 
havior of  fire  clays  is  recognized  in  a  tentative  scheme  of  classifica- 
tion presented  by  the  present  writer  and  Mr.  Moore.1 

It  will  be  noted  from  Fig.  30  that  these  clays  show  comparatively 
little  decrease  in  porosity  from  cone  010  to  cone  11.  This  decrease 
averages  from  7  to  15  per  cent  of  the  initial  porosity  and  in  no  case 
does  it  exceed  17  per  cent. 

The  specific,  gravity,2  as  shown  in  Fig.  31  remains  fairly  constant 
from  cone  010  to  cone  3  and  then,  even  in  the  purest  clays,  it  begins 
to  decrease  slightly.  This  decrease  in  specific  gravity  in  the  No.  1 
fire  clays,  even  when  the  porosity  remains  very  high,  is  considered  as 
evidence  of  the  influence  of  the  adsorbed  or  cementing  salts  .which, 
while  constituting  but  a  very  small  part  by  weight  of  the  whole,  are 
nevertheless  potent  factors  in  causing  fusion. 

1  Trans.  Am.   Soc,  Vol.  IX,  pp.   239. 

2  The  specific  gravity  here  referred  to  is  the  specific  gravity  of  that  portion  of 
a  saturated  brick  not  occupied  by  water.  Inasmuch  as  this  water  impermeable 
mass  very  often,  in  fact,  in  the  case  of  impure  clays  generally  does  contain  in- 
closed or  sealed  pores  known  as  blebs,  the  specific  gravity  so  obtained  cannot  be 
the  actual  specific  gravity  of  the  material  of  which  this  water  impermeable  portion 
consists.  The  true  specific  gravity  of  the  material  can  be  obtained  by  crushing  the 
brick  to  fine  powder,  thus  eliminating  the  sealed  pores,  and  then  determining  the 
specific  gravity  of  the  powcer  in  a  specific  gravity  bottle  as  before  described.  For 
this  reason,  the  writer  has  classified  specific  gravities  under  three  heads:  First, 
false  specific  gravity,  or  the  weight  per  unit  volume  of  the  whole  brick ;  Second, 
apparent  specific  gravity,  or  the  weight  per  unit  volume  of  the  water-impermeable 
mass;  Third,  true  specific  gravity,  or  weight  per  unit  volume  of  solid  material  in 
the  water-impermeable  mass. 


272 


PAVING    BRICK    AND    PAVING    BRICK   CLAYS. 


[BULL.   NO.    £ 


.OS 


.04  .02  1  3  5  7 

TEMPERATURES  EXPRESSED  IN  CONES 


11 


Fig.    31.     Curves   showing   changes   in   specific   gravity   of   fire   clays   with   pro- 
gressive  intensity  of  heat  treatment. 

Number  Two  Fire  Clays — It  will  be  noted  that  while  the  decrease  in 
specific  gravity  of  this  group  of  clays  is  about  the  same  as  that  shown 
in  the  No.  1  fire  clays,  the  porosity  shows  a  much  larger  decrease.  The 
earthy  vitrification  and  slow  fusion  is  quite  pronounced  in  this  group, 
•permitting  their  use  in  the  paving  brick,  sewer  pipe,  stoneware  and 
terra-cotta  industries,  but  not  in  the  manufacture  of  No.  1  fire  brick. 

Number  Three  Fire  Clays— In  Figs.  27  and  28  are  shown  the  limiting 
area  of  porosity  and  specific  gravity  curves  of  a  class  of  clays  which, 
in  the  judgment  of  the  writer,  ought  to  be  put  in  a  different  category 
•from  the  preceding  group,  or  number  two  fire  clays.  Heretofore,  both 
have  been  classed  together  indiscriminately  in  ceramic  and  geological 


PL'RDY] 


PYRO-PHYSICAL    AND    CHEMICAL    PROPERTIES. 


273 


literature,  as  number  two  fire  clays,  but  they  are  not  the  same.  Clays 
of  this  class  differ  from  the  No.  1  and  No.  2  fire  clays,  in  that  they 
seldom  have  a  fusion  point  exceeding  cone  16  or  17,  fuse  in  a  very  irreg- 
ular manner,  and  exhibit  a  much  larger  decrease  in  specific  gravity 
owing  probably  to  the  presence  of  iron  in  nodular  form  as  sulphides  or 
carbonates. 

Fire  Clays  in  General — These  conclusions  may  be  summarized  as  fol- 
lows: First,  While  all  the  types  of  fire  clays  here  tested  maintained 
the  same  range  in  porosity  up  to  cone  010,  there  is  a  marked  differ- 
entiation of  each  at  cone  08.  Second,  From  cone  08  to  about  cone  1 
the  No.  2  and  No.  3  fire  clays  traverse  a  common  area,  but  at  cone  1 
•the  No.  3  type  begins  to  fuse  more  rapidly,  until  when  cone  7  is 
reached,  the  No.  3  fire  clays  have  fused  sufficiently  to  be  wholly  differ- 
entiated from  the  No.  2.  Third,  Since  the  porosity  curves  in  Fig.  27 
are  composite  curves  showing  the  limits  of  variation  in  the  few  clays 
tested,  it  is  possible  that  broader  limits  will  be  determined  when  more 
and  a  larger  variety  of  clays  are  tested,  yet  the  data  here  presented  are 
sufficient  to  demonstrate  that  where  chemical  analysis  and  fusion  period 
determinations  have  failed,  this  method  of  differentiation  has  proved 
successful.  Fourth,  Differentiation  of  fire  clays  on  the  basis  of  specific 
changes  will  hardly  be  possible  on  account  of  the  limited  differences 
between  the  areas  traversed  by  the  specific  gravity  curves  of  each  type  of 
fire  clay,  yet  as  is  shown  in  Fig.  28  the  specific  gravity  curves  parallel 
and  diverge  from  one  another  at  about  the  same  temperatures  as  do 
the  porosity  curves  in  Fig.  27. 

Chemical  analysis  and  points  of  fusion  of  a  few  of  the  fire  clays  from 
which  curves  were  drawn  are  as  follows: 

Table  XLIII. 

No.  1 — Fire  Clays. 


jSSgiJl     Moisture. 

Volatile 
Matter. 

Si02 

Al2Oa 

Fe203 

Ti02 

Total. 

Fusion 
point. 

H-24.... 
V-11.... 
F-18.... 
F-19... 

0.6 
1.74 
0.84 
1.19 

4.63 
10.28 
6.66 
6.31 

76.10 
56.28 
66.88 
68.12 

15.31 
26.68 
21.87 
20.08 

1.10 
3.24 
2.23 
1.76 

1.31 
1.29 
1.18 
1.16 

99.06 
99.50 
99.86 
98.62 

30 

Not  reached. .. 

29 

31 

Table  XLIV. 

No.  2 — Fire  Clays. 


Sample        iffnfatm* 
Number.      Moisture. 

Volatile 
Matter. 

Si02 

A1203 

Fe203 

Ti02 

Total. 

[Fusion 
point. 

V-4  .... 
K-12.... 

2.37 
0.60      . 

8.84 
10.09 

54.80 
54.37 

29.44 
23.61 

1.70 
6.14 

0.82 
x5.97 

97.97 
1C0. 78 

Not  reached. .. 
..do 

l  Total  fluxes  TiO,  was  not  determined  in  K-12. 


■18  G 


274  PAVING   BRICK   AND    PAVING   BRICK   CLAYS.  [bull.  no.  9 

Chemical  analyses  were  not  made  of  all  the  clays  of  the  No.  1  and 
No.  2  type  and  none  of  the  No.  3.  From  the  few  that  were. made,  how- 
ever, it  is  evident  that  refractoriness  and  slow  fusion  are  not  always  de- 
pendent upon  the  proportional  content  of  alumina  and  silica,  for  the 
two  No.  2  fire  clays  have  on  the  average  higher  AkCh  and  lower  SiO: 
content  that  the  No.  1  fire  clays.  This  is  directly  contrary  to  our  past 
teachings  and  contrary  to  what  might  be  expected  from  Segar's  AbOs- 
SiOa  curve,  as  shown  in  figure  19,  page  208. 

Paving  and  Building  Brick  Clays — The  standardization  of  tests  for 
first-class  paving  brick  clays  has  been  and  perhaps  will  be  for  some  time 
the  subject  of  consideration  by  ceramic  investigators.  The  pyro-physi- 
cal  and  chemical  tests  here  reported  can  be  said  to  give  negative  rather 
than  positive  information,  in  that  they  very  effectively  differentiate  the 
clays  they  cannot  from  those  that  may  be  utilized  in  paving  brick  man- 
ufacture. Judging  from  the  results  so  far  obtained,  they  fail,  how- 
ever, to  differentiate  the  paving  brick  clays  one  from  another  in  re- 
gard to  their  comparative  quality.  For  example,  we  have  not  been 
able  to  distinguish  by  these  tests  between  the  clays  of  14  per  cent  and  the 
24  per  cent  type,  measured  in  per  cents  of  loss  in  the  rattler  test,  nor 
between  the  clays  that  preserve  their  maximum  strength  through  a 
wide  heat  range  and  those  which  attain  and  preserve  their  maximum 
strength  only  within  a  very  narrow  heat  range. 

The  cause  of  failure  of  the  pyro-chemical  studies  in  this  respect  is, 
no  doubt,  to  be  found  in  the  fact  that  inherent  strength  is  not  wholly 
a  function  of  rate  of  vitrification  or  development  of  vesicular  structure. 
As  shown  in  earlier  pages,  physical  tests  on  the  raw  clays  failed  to  dif- 
ferentiate paving  from  building  brick  clays.  The  pyro-chemical  studies 
here  reported  are  the  only  ones  that  give  any  clue  to  cause  of  toughness 
or  strength  of  the  burned  ware. 

Pyro-chemical  studies  similar  to  those  here  outlined,  together  with  a 
determination  of  the  maximum  strength  and  the  range  of  temperature  in 
which  this  maximum  strength  is  developed,  would  enable  the  observer 
to  properly  classify  and  differentiate  paving  brick  clays.  This,  however, 
amounts  to  a  sub-classification  of  the  paving  clays  on  a  basis  different 
from  that  of  the  main  sub-division. 

The  striking  differences  between  the  building  and  paving  brick  clays 
are  apparent  from  figures  32  and  33.  Earlier  vitrification,  irregularity 
in  decrease  of  porosity  and  specific  gravity,  apparently  larger  quantity 
of  vessicular  glass  formed  within  the  mass,  or  at  least  a  more  notable 
bloating,  due  to  volatilization  of  certain  constitutents,  probably  the  sol- 
uble and  adsorbed  salts,  are  the  distinguishing  features  of  trie  strictly 
building  brick  class. 

Sufficient  evidence  is  at  hand  to  warrant  the  statement  that  any  clay 
which  vitrifies  to  a  porosity  of  2  or  3  per  cent  before  cone  5  is  reached, 
in  the  heat  treatment  prescribed  in  this  method  of  burning  test  pieces, 


PURDY] 


PYRO-PHYSICAL    AND   CHEMICAL    PROPERTIES, 


275 


will  be  too  brittle  for  use  as  paving  brick  material,  no  matter  how  little 
vesicular  structure  is  developed.  The  fact  is,  however,  that  it  will  be  a 
rare  case  in  which  vesticular  structure  is  not  strongly  developed  if  the 
clay  shows  an  early1  and  rapid  rate  of  vitrification. 

In  figures  32  and  33  are  shown  the  upper  and  lower  limits  of  areas 
that  were  traversed  respectively  by  the  porosity  and  specific  gravity 
curves  of  clays  that  either  are  being  or  can  be  used  for  the  purposes  in- 
dicated in  the  figures. 


06  ^Oi  ~tt  I  3  5 

TEXPERA  TURES  EXPRESSED  IN  CONES 

Fig.    32.    'Curves   showing   changes    in   porosity   of   paving   and   building   brick 
clays  with  progressive  intensity  of  heat  treatment. 


1  The  use  of  the  comparative  terms  "early"  and  "rapid"  in  reference  to  this 
type  of  clays,  in  contrast  to  their  relative  use  in  regard  to  fire  clays,  is  best  illus- 
trated by  reference  to  the  curves. 


276 


PAVING    BRICK   AND    PAVING   BRICK   CLAYS. 


[BULL.   NO.   9 


.06  .04  .02  1  3  5 

TEMPERA  TV  RES  EXPRESSED  IN  CONES 


Fig.    33. 


Curve    showing   changes   in   specific   gravity  of   paving   and   building 
brick  clays  with  progressive  intensity  of  heat  treatment. 

The  boundary  limits  shown  in  these  figures  are  those  obtained  in 
these  tests,  and,  therefore,  may  not  show  exactly  the  true  limits  of"  the 
several  areas.  They  indicate,  however,  approximately  the  relative  man- 
ner in  which  the  clays  used  for  the  several  industries  behave  in  fusing. 

AIL  clays  used  for  paving  and  sewer  brick  may  be  used  for  building 
brick,  but  what  are  here  defined  as  strictly  building  brick  clays  cannot 
be  used  for  paving  or  sewer  brick.  All  paving  brick  clays  can  be  used 
in  the  manufacture  of  sewer  brick,  but  the  sewer  brick  clays  cannot 
be  used  for  paving  brick.  The  points  of  differentiation  are;  first,  the 
paving  brick  clay  fuses  more  slowly  and  decreases  less  in  specific  gravity ; 


PURDYJ  PYRO-PHYSICAL    AND   CHEMICAL    PROPERTIES.  277 

second,  the  sewer  (and  side  walk)  brick  clay  fuse  more  rapidly  but 
maintain  their  shape  through  a  considerable  range  of  heat  treatment 
before  failing;  third,  those  clays  which  are  fit  only  for  building  brick 
vitrify  rapidly  and  fail  as  soon  as,  or  before  they  are  completely  vitri- 
fied. The  sewer  brick  clays  can  be  brought  with  safety  to  complete 
vitrification  without  much  danger  of  loss  except  perhaps  from  "kiln 
marking"  while  those  clays  which  are  fit  only  for  building  brick  bloat 
and  become  spongy  as  well  as  soft  almost  as  soon  as  vitrification  takes 

place. 

Since  the  tracing  of  the  porosity  curves  through  the  upper  or  paving 
brick  clay  area  does  not  necessarily  signify  that  they  are  good  for  paving 
brick  manufacture,  the  lower  limit  may  appear  to  be  superfluous.  It 
remains  a  fact,  however,  that,  according  to  the  tests  here  reported,  a 
clay  must  have  its  porosity  curve  confined  within  the  limiting  bound- 
aries shown  in  order  to  develop  the  required  toughness.  So  far  as  ex- 
perience with  the  Illinois  clays  is  concerned,  the  curves  for  porosity 
and  specific  gravity  in  figure  29  and  30  respectively,  denote  quite  rig- 
idly the  allowable  variation  in  rate  of  decrease  in  porosity  and  specific 
gravity. 

GENERAL  CONCLUSION. 

In  the  preceding  discussions  of  physical,  chemical,  and  pyro-physical 
and  chemical  properties  of  clays  all  of  the  relations  between  these  prop- 
erties that  were  known  or  observed  have  been  shown.  A  review  of  these 
discussions  reveals  the  following  as  being  the  most  important. 

1.  Measurement  of  some  of  the  properties  failed  to  give  results  that 
show  the  factors  which  affect  them  or  which  are  involved  with  them. 
This  was  made  plain  in  case  of  the  "individual  grains"  as  obtained  by 
mechanical  analysis.  We  have  seen  that  the  methods  universally  em- 
ployed to -effect  "the  physical  disintegration  of  clay  are  not  sufficiently 
intensive  to  produce  complete  disintegration.  It  has  also  been  demon- 
strated that  the  grains  or  particles  so  obtained  do  not  usually  consist 
of  one  mineral  substance.  As  a  consequence  of  this  cementation  of 
smaller  particles  of  different  substances  into  bundles  or  groups,  any  in- 
ference or  conclusion  based  on  fineness  of  grain  cannot  be  very  general 

in2aPPUltimate  analysis  or  gross  rational  analysis  of  clay  cannot  reveal 
qualities  that  affect  either  the  "working"  or  "burning"  properties 

3  Either  ultimate  or  rational  analysis  of  the  several  groups  ol  grains 
may  reveal  some  important  relation  of  constitution  to  manifested  prop- 
erties This  however,  remains  to  be  demonstrated.  It  can  be  said 
however,  that  such  determinations  will  not  likely  become  "commercial 
tests  of  clays.  On  the  other  hand,  however,  it  seems  certain  that  they 
will  be  valuable  for  research  purposes".  . 

4  Vitrification  behavior,  rate  of  fusion  or  toughness  of  bricks,  do 
not  seem  to  depend  within  any  but  very  wide  limits  or  m  any  traceable 
manner  upon  chemical  or  mineralogical  constitution  of  clay.  _ 

5  No  combinations  of  physical  and  chemical  properties  can  be  said 
to  be  essential  to  clays  from  which  first-class  paving  brick  may  be 
manufactured.. 


278  PAVING    BRICK   AND    PAVING    BRICK   CLAYS.  [bull.  no.  9 

6.  The  most  satisfactory  tests  tried  or  developed  during  the  course 
of  these  researches  for  distinguishing  between  clays  on  the  basis  of  their 
commercial  availability  are  rate  of  decrease  in  porosity  and  specific 
gravity.  While  even  these  tests,  so  far  as  can  be  judged  by  our  results, 
do  not  make  an  absolute  discrimination,  the  discussions  and  curves  here 
given  make  plain  the  fact  that  such  tests  are  the  most  serviceable  of  any 
so  far  developed.  The  other  tests  have  special  uses  and  are  not  to  be 
entirely  condemned. 

7.  Toughness  of  brick  does  not  bear  a  consistent  relation  to  degree 
or  range  of  vitrification.  Each  clay  has  its  own  peculiar  range  and  de- 
gree of  vitrification  at  which  its  maximum  toughness  is  developed.  In 
some  clays  this  range  is  very  small  and  in  some  quite  large.  In  some 
clays  maximum  toughness  is  attained  when  the  brick  still  shows' an  ab- 
sorption of  8  or  12  per  cent  and  in  others  not  until  the  absorption  has 
been  decreased  to  2  or  4  per  cent.  No  tests  other  than  the  "rattler  test" 
on  full  size  brick  which  have  been  burned  with  different  intensity  of  heat 
treatment  have  brought  out  data  which  bear  on  this  peculiarity  of  clays. 

8.  The  pyro-physical  studies  which  have  been  described  suggest  a 
series  of  determinations  which  should  be  more  valuable  in  that  they 
ought  to  reveal  .the  cause  for  this  want  of  correlation  of  toughness  and 
vitrification  behavior.  The  series  of  determinations  referred  to  is  that 
of  the  volume  changes  which  take  place  with  increasing  intensity  of 
heat  treatment.1 

The  volume  changes  which  are  important  are: 
(a)   exterior  volume  of  brick, 
(b).  volume  of  skeleton  of  brick. 

(c)  volume  of  open  pores. 

(d)  volume  of  sealed  pores 

1  See  Trans.   Am.-  Cer.   Soc,  Vol.  X. 


CLAYS   STUDIED   WHICH    ARE    SUITABLE    FOR    USE    IN 

THE  MANUFACTURE  OF  PAVING  BRICK. 

[Compiled  by  C.  W.  Rolfe.] 

Introduction. 

The  clays  especially  studied  for  the  purposes  of  this  report  are  listed 
below.  They  are,  with  few  exceptions,  now  being  used  in  the  manu- 
facture of  pavers  of  proved  excellence. 

While  the  writer  believes  that  most  counties  in  the  State  contain 
clays  from  which  high  grade  pavers  could  be  made,  if  the  materials 
were  properly  handled,  there  are  only  eight  localities  where  this  is 
actually  done.  This  is  probably  due  to  the  facts,  that  there  is  no  very 
large  demand  for  pavers ;  that  both  Indiana  and  Iowa  have  large  plants 
•near  the  borders  of  this  State;  that  commercial  considerations  which  are 
in  no  way  influenced  by  the  qualities  of  the  clays  favor  these  plants; 
and  also  to  a  large  extent  because  no  systematic  survey  of  our  clays 
has  been  made  and  so  their  qualities  are  not  known. 

In  order  to  give  the  reader  a  clearer  idea  of  the  qualities  a  paving- 
brick  clay  should  possess,  it  was  decided,  because  the  Illinois  factories 
are  so  few,  to  include  a  number  of  those  which  are  making  first  class 
pavers  in  the  neighboring  states  of  Ohio,  Indiana,  Iowa,  Missouri  and 
Kansas.  All  the  Illinois  clays  now  used  for  pavers  are  from  the  coal 
measures,  and  many  people  have  an  idea  that  shales  from  this  horizon 
•furnish  the  only  material  suitable  for  the  manufacture  of  such  wares. 
The  clays  used  in  these  other  states  are  from  various  horizons,  and,  as 
will  be  seen  by  a  comparison  of  the  tables  below,  they  possess  qualities 
in  every  way  equal  to  the  coal  measure  shales  used  in  Illinois. 

Preliminary  tests  were  made  on  a  considerable  number  of  samples 
covering  a  large  part  of  the  State.  These  tests  were  made  on  small 
samples  taken  usually  from  more  or  less  weathered  outcroppings.  Such 
tests  are  always  unsatisfactory  because  the  samples  are  not  large  enough 
to  permit  studies  which  will  give  decisive  results,  and  also  because  the 
changes  which  occur  in  weathering  usually  tend  to  destroy  those  qual- 
ities of  a  clay,  which  make  it  desirable  for  the  manufacture  of  pavers. 
TVhile  the  tests  made  indicated  that  a  considerable  percentage  of  the 
clays  tested,  some  30  or  40  in  all,  were  suited  to  the  manufacture  of 
pavers,  the  limitations  under  which  the  work  was  conducted  made  it 
impossible  to  carry  out  complete  studies  on  any  large  number  of  samples. 
H1G — H23  are  examples  of  such  clays. 

279 


280  PAVING    BRICK   AND    PAVING   BRICK   CLAYS.  [bull.  no.  9 

It  is  hoped  that  at  a  future  time  studies  of  a  larger  series  of  un- 
weathered  clays,  taken  from  all  parts  of  the  State  and  from  as  many 
geological  horizons  as  possible,  may  be  carried  on  with  the  result  of 
demonstrating  possibilities  for  the  use  of  Illinois  clays  now  recognized 
only  by  those  who  have  studied  the  problem  from  the  geological  side. 
It  is  the  belief  of  the  author  that  there  is  no  considerable  section  of  the 
■State  that  will  not  furnish  clays  well  adapted  to  the  manufacture  of 
•pavers  if  skillfully  handled.  This  opinion  is  based  on  the  results  of 
•tests  made  in  our  laboratories,  but  whose  character  was  not  such  as  to 
warrant  publication  of  the  results. 

DESCRIPTION  OF  DEPOSITS. 

Descriptions  of  the  deposits  from  which  the  clays  studied  were 
taken  will  be  found  below.  The  samples  were  taken  from  the  clay 
which  had  passed  the  dry  pan  and  was  ready  for  the  pug-mill. 

K  1 — This  clay  is  used  by  the  Alton  Paving  Brick  Co.  in  the  manufacture 
of  paving  blocks  and  dry  pressed  building  brick. 

A  section  taken  from  the  bank  is  as  follows: 

Feet 

Loess     2-20 

Yellow   sandy   clay    8 

Soft   sandstone    4 

Sandy  blue  shale • 12 

Coal      4 

Fire    clay     18 

The  shale  alone  makes .  a  very  tough  brick  but  it  is  found  desirable  to 
mix  with  it  more  or  less  of  the  overlying  materials.  The  loess  is  principally 
used  in  making  dry  pressed  building  brick.  The  sandstone  and  all  strata 
belong  to  the  coal  measures. 

K  2 — This  is  a  coal  measure  shale  used  by  the  Hydraulic  Press  Brick  Co. 
of  St.  Louis,  Mo.,  in  the  manufacture  of  pavers  at  their  factory  near  Glen 
Carbon,  111.  The  deposit  is  about  30  feet  thick  and  consists  of  thick  beds 
of  shale  separated  by  bands  of  sandy  shale  and  sandstone. 

K  3 — Used  by  the  Albion  Vitrified  Brick  Co.,  at  Albion,  111.,  in  the  manu- 
facture of  paving  blocks,  which  are  used  to  some  extent  also  in  building. 
The  works  are  situated  a  short  distance  from  the  town  on  the  Southern  Rail- 
road. 

A  section  of  the  bank  shows: 

Feet 

Yellow  clay 6 

Argillaceous    sandstone    8 

Soft  blue  shale  with  thin   partings  of  sandstone    2 

Hard  blue   shale    22 

Softer  blue  shale   4 

This  clay  required  thorough  pugging  under  heavy  pressure  to  produce  the 
best  results.     The  sandstone  and  shales  belong  to  the  coal  measures. 

K  4 — This  highly  plastic  shale  from  the  coal  measures  is  used  by  the 
Springfield  Paving  Brick  Co.,  in  the  manufacture  of  paving  blocks  exclu- 
sively.   The  works  are  located  near  Springfield,  111. 

A  section  of  the  bank  shows: 

Feet 

Vellow  loess-like  clay 6-8 

Weathered  shale   6 

Blue  compact  shale   " 45 

The  shale  includes  a  thin  seam  of  coal.  Rapid  pugging  under  light  pres- 
sure seem  to  produce  the  best  results  with  this  clay.  It  will  be  noticed  that 
the  material  used,  which  includes  all  shown  in  the  above  section,  is  entirely 
free  from  sandstone  or  sandy  layers. 


ROLFE] 


CLAYS    STUDIED.  281 


K  5— This  clay,  which  is  used  by  the  Banner  Clay  Co.,  of  Edwardsville, 
111.,  for  the  manufacture  of  paving  blocks,  lies  under  a  heavy  overburden  of 
loess  and  drift  often  aggregating  25  to  40  feet  in  thickness.  The  shale  from 
which  the  brick  are  made  belongs  to  the  coal  measure  series  and  is  exposed 
only  in  the  bluffs  of  streams  which  run  in  deep  valleys.  The  shale  is  all 
more  or  less  sandy  and  is  composed  of  alternating  layers  of  harder  and 
softer  material. 

A  section  at  the  bank  shows: 

Feet 

Loess-like  clay 1 2 

Yellow    clay    8 

Tough  blue  clay  ° 

Sandy  shale  in  alternating  harder  and  softer  layers   36 

K  6 — The  Purington  Paving  Brick  Co.  of  Galesburg,  111.,  have  probably  the 
largest  plant  in  the  State  devoted  to  the  manufacture  of  paving  blocks  and 
paving  and  building  brick.  Their  annual  output  is  about  90,400,000  of  which 
about  80,000,000  are  pavers.  In  spite  of  its  sandy  character  and  moderate 
plasticity  it  yields  readily  to  the  methods  of  manufacture,  and  makes  a  com- 
pact body  of  excellent  quality. 

The  section  of  the  bank  shows: 

Feet 

Glacial  drift 18 

Weathered  shale    (not  used)    12 

Blue  shale  with  thin  partings  of  soft  sandstone   60 

The  shale  belongs  to  the  coal  measure  series,  and  lies  between  the  horizons 
of  "coals  3  and  4." 

K  7 — This  clay,  which  lies  immediately  above  "coal  7,"  is  used  by  the 
Streator  Paving  Brick  Co.,  at  Streator,  111.,  in  the  manufacture  of  brick  and 
blocks  which  are  used  for  paving  and  for  the  facing  of  buildings. 

A  section  of  the  bank  appears  below: 

Feet 

Glacial  deposits  consisting  of  loess-like  clay,  yellow  and  blue  clays   20 

Blue  shale  with  nodules  and  thin  partings  of  sandstone   30 

Goal   4-5 

Fire  clay 

The  glacial  deposits  are  stripped  and  the  shale  and  sandstone  alone  are 
used  in  the  manufacture  of  brick. 

K  15 — Lies  immediately  above  "coal  7."  The  bank  is  located  near  Streator, 
111.,  and  is  operated  by  the  Barr  Clay  Co.,  in  the  manufacture  of  paving 
and  building  brick  of  good  quality. 

A  section  of  the  bank  follows: 

Feet 

Glacial  deposits,  loess-like,  and  yellow  and  blue  clay,  gravel,  sand,  etc 5-15 

Sandstone     2-3 

Sandy   blue   shale   in  thin  layers    5-10 

Sandy   blue    shale,    massive    10-20 

"Very  fine   grained,   plastic  blue  shale    10-12 

Coal     4-5 

The  glacial  deposits  are  rejected.  All  the  other  strata  are  mixed  and  used 
in  making  the  brick. 

K  14 — The  Western  Brick  Co.,  of  Danville,  111.,  uses  this  material  for  the 
manufacture  of  building  and  paving  brick.  They  have  one  of  the  largest 
and  most  successful  plants  in  the  State. 

A  section  of  the  bank  follows: 

Feet 

1.  Glacial  deposits,  variable  thickness   2-33 

2.  Shale  with  sandstone  partings   50 

3.  Coal,    No.    7    6 

4.  Fire    clay    • ••  •  . .        2 

5.  Thin  layers  of  coal  and  fire  clay    3 

6.  Fire    clay    5 

7.  Clay  rich  in  lime    10 

8.  Clay    with    layers    of    limestone     6 

9.  Coal,   No.    6    8 

10.     Fire  clay    6 


282  PAVING   BRICK   AND    PAVING   BRICK   CLAYS.  [bull.  no.  9 

11.  Sandstone   10 

12.  Sandy   shale    25 

13.  Shale    200 

Building  brick  are  manufactured  from  No.  2  as  a  whole.  The  lower  half 
of  No.  2  is  used  for  pavers.    Nos.  12  and  13  are  reached  by  shaft. 

F  1 — The  Danville  Brick  and  Tile  Co.,  manufacturers  pavers  from  No.  12 
of  the  section  shown  under  K  14.    This  deposit  outcrops  near  their  plant. 

H  16 — Is  a  blue  coal  measure  shale  from  the  pit  of  Mr.  Carter  at  East 
Peoria. 

H  17 — This  clay  was  obtained  from  the  bank  of  the  LaSalle  Pressed  Brick 
Co.,  near  LaSalle,  111.  It  is  not  now  used  for  the  manufacture  of  pavers. 

Feet 

1.  Stripping 12 

2.  Sidewalk   clay  v   2    10 

3.  Green  clay  v   1 7 

4.  Clay  with  much  pyrites    5 

5.  Red  burning-  clay  H  17 14 

The  indications  are  that  v  1  and  2  and  H  17,  if  mixed,  could  be  used  in 
making  pavers  of  good  quality. 

H  18 — From  a  weathered  outcrop  probably  40  feet  thick  situated  one  mile 
east  of  the  station  of  the  C.  &  N.  W.  R.  R.  at  Sterling,  111.  It  belongs  to  the 
-Cincinnati  (Maquoketa)  series  of  the  Lower  Silurian  (Ordovician).  The 
indications  are  that  it  would  probably  make  good  pavers. 

H  20 — Cincinnati  shale  from  the  farm  of  Dupiers  &  Son,  near  Savannah, 
111.  It  is  a  weathered  sample  and  unless  the  unweathered  portion  should 
make  a  better  showing,  is  worthless  as  material  for  pavers. 

H  23— Is  from  the  bank  of  the  Argillo  Works  at  Carbon  Cliff,  111.  Would 
probably  make  good  pavers. 

H  21 — This  sample  of  Cincinnati  shale  came  from  the  west  end  of  the 
tunnel  of  the  Great  Western  R.  R.  near  Rodden,  111.  Aside  from  its  fine- 
ness of  grain  the  material  seemed  to  be  well  adapted  to  the  manufacture  of 
pavers.  As  the  sample  was  from  a  weathered  outcrop  it  is  possible,  perhaps 
probable,  that  the  unweathered  material  could  be  so  treated  as  to  overcome 
this  difficulty. 

K  8 — This  is  a  Carboniferous  shale  used  by  the  Wabash  Clay  Co.,  of  Ved- 
ersburg,  Ind.,  in  the  manufacture  of  paving  blocks.  The  material  hereto- 
fore used  is  a  mixture  from  two  banks,  one  located  one  mile  north  and  the 
other  one  and  one  half  miles  south  of  the  plant.  As  the  use  of  material 
from  the  north  bank  is  soon  to  be  discontinued,  the  material  tested  and  the 
section  given  below  are  from  the  south  bank  alone. 

Feet 

1.  Surface  deposits    4 

2.  Rotten  yellow  sandstone 12 

3.  Shale  varying  from  hard  to  soft,  and  in  color  from  very  light  to  black   ...        24 

4.  Fine    grained    dark    shale    10 

5.  Coal     1-1  % 

K  9 — This  shale,  used  by  the  Poston  Paving  Brick  Co.,  at  Crawfordsville, 
Ind.,  for  the  manufacture  of  pavers,  belongs  to  the  Knobstone  formation 
of  the  Lower  Carboniferous  or  Mississippian  series.  The  material  has  but 
little  plasticity,  but  when  burned  makes  blocks  of  excellent  quality. 

The  section  is  as  follows: 

Feet 

1.  Surface    deposit,    gravel    and   clay    : 14  " 

2.  Shale,  very  constant  in  quality,  except  that  the  lower  12  feet  are  harder  than 

the   rest.      (This  shale   contains  more   or  less  nodules  which  are  separated 
before   the    clay   is   used) 35 


rolfe]  CLAYS   STUDIED.  283 

1.  Soil    and   joint    clay ♦> 

2.  Sandy  shale • ■  •  ,3 

K  11— The  Terre  Haute  Vitrified  Brick  Co.,  of  Terre  Haute,  Ind.,  uses  this 

shale  in  the  manufacture  of  paving  and  building  brick  of  excellent  quality. 
This  material   comes  from  the  Coal  Measures  immediately  above  "Coal  7." 
The  section  of  the  bank  follows: 

Feet 

3.  Lig-ht  gray  shale  with  hands  of  limestone  and  ironstone  nodules    12 

4.  Dark  shale  with  hard  oolitic  nodules    14 

5.  Coal,   No.    7    5 

6.  Fire    clay    

The  margin  of  vitrifaction  is  narrow. 

K  11 — The  Indiana  Paving  Brick  and  Block  Co.,  of  Brazil,  Ind.,  uses  this 
material  in  the  manufacture  of  paving  block. 
The  section  at  the  plant  is  as  follows: 

Feet 

1 .  Buff  colored   clay 8 

2.  Grey  and  yellow  clay   J* 

3.  Stoneware   clay    •  •  •  • , • y 

4.  Shale  with  cubic  cleavage  containing  harder  layers  and  kidney-shaped  con- 

cretions         24 

5.  Coal 1% 

6.  Fire    cla  y 

K  12 — This  is  a  fire  clay  coming  from  below  the  coal  in  the  section  above. 

K  13— The  Clinton  Paving  Brick  Co.,  of  Clinton,  Ind.,  uses  this  material 
in  the  manufacture  of  paving  blocks.  It  lies  just  below  the  upper  Clinton 
coal. 

The  section  at  the  bank  follows: 

Feet 


30 


1.  Fire    clay     

2.  Sandstone     , ■ 

3.  Dark   blue  or  gray  shale  with  nodules  of  pyrites,   large   above   and  smaller 

below     

4.  Shale  with  thin  layers  of  limestone    ° 

5.  Fine,  fat,  massive,  black  shale    z* 

6.  Hard  black  shale    f 

7.  Coal 1% 

8.  Fire    clay z 

R  1 — This  impure  fire  clay,  obtained  by  mining  just  below  their  coal  No. 

5,  is  used  by  The  Nelsonville  Brick  Co.,  Nelsonville,  Ohio,  in  the  manufacture 
of  paving  block  and  some  building  brick.  Their  annual  output  is  about 
25,000,000  blocks. 

R  2— This  is  a  shale  from  an  outcrop  of  the  Subcarboniferous  near  Ports- 
mouth, Ohio,  and  is  used  by  the  Portsmouth  Paving  Brick  Co.,  in  the  manu- 
facture of  their  Hallwood  Block. 

R  3  and  4 — These  are  shales  obtained  from  near  the  base  of  the  Coal 
Measures  at  Canton,  Ohio,  and  used  by  the  Metropolitan  and  Cleveland  and 
Canton  Paving  Brick  Companies  in  the  manufacture  of  paving  blocks,  with 
an  output  of  about  500,000  per  day. 

g  i— These  Coal  Measure  shales  are  used  by  the  Moberly  Brick,  Tile  and 
Earthenware  Co.,  in  the  manufacture  of  building  brick  and  paving  blocks, 
at  Moberly,  Mo. 

Section  of  bank: 

Feet 

1.     Soil     2 

7.     Loess     .  . %" 

3.  Dark,  thin  layered  shaly  sandstone    j" 

4.  Fine  grained  bluish  gray  shale  with  sandy  layers 6U 

5.  Mixture  1-5  dark,   4-5  blue  shale    

S  2— These  are  Coal  Measure  shales  used  by  the  Kansas  City  Hydraulic 
Pressed  Brick  Co.,  at  Diamond,  Mo.,  eight  miles  from  Kansas  City.  This  clay 
is  mined  and  consists  of  a  layer  20  feet  in  thickness  of  which  the  upper  4 
feet  is  quite  sandy  while  the  lower  16  feet  is  a  fine  grained,  grayish  blue 
shale.     The  two  grades  are  used  in  the  proportions  indicated:   i.  e.  1  to  4. 


284 


PAVING    BRICK    AND    PAVING    BRICK   CLAYS. 


[BULL.   NO.    9 


L  2 — This  material  is  used  by  the  Lawrence  Vitrified  Brick  and  Tile  Co., 
of  Lawrence,  Kans.,  in  the  manufacture  of  both  building  brick  and  pavers. 
Section  of  bank: 

Feet 

1.  Red   quartz    sand    5 

2.  Shale,   yellow  above,   blue  below    20 

S.     Mixture  11-12  shale,   1-12   sand  ■ 

B  2 — The  Atchison  Paving  Brick  Co.,  of  Atchison,  Kans.,  uses  this  material 
in  the-  manufacture  of  building  and  paving  brick. 
Section  of  bank: 

Feet 

1.  Limestone     4 

2.  Yellow    shale     14 

3.  Soft    sandstone    5 

4.  Sandy   shale    (50    per   cent   sand) 16 

5.  Blue    shale    11 

For  pavers  Nos.  4  and  5  are  mixed  in  such  proportions  as  to  make  J 
sand  and  §  shale.  They  also  try  to  combine  Nos.  2,  3  and  5  so  as  to  give 
the  same  mixture. 

G  2— This  shale  is  used  by  the  Coffeyville  Brick  and  Tile  Co.,  Coffeyville, 
Kans.,  in  the  manufacture  of  paving  blocks  exclusively. 

Section  of  bank: 

Feet 

1.  Stripping,    gravel,   clay  and  limestone    10 

2.  Shale,    very    uniform    : 90 

I  2 — This  material  is  used  by  the  Caney  Vitrified  Brick  Co.,  of  Caney, 
Kans.,  in  the  manufacture  of  building  brick  and  such  pavers  as  may  be 
needed  for  local  consumption.  The  surface  of  the  shale  where  it  is  weathered 
is  yellow  in  color  but  becomes  blue  with  depth.  The  thickness  of  the  deposit 
has  never  been  ascertained.  It  is  covered  with  a  thin  layer  of  soil  which  is 
stripped. 

H  2 — This  shale  is  used  by  the  Capital  City  Vitrified  Brick  and  Paving 
Co.,  in  the  manufacture  of  pavers,  near  Topeka,  Kans. 

Section  of  bank: 

1.  Surface   soil    3 

2.  Limestone     1 

3.  Yellow   clay 1 

4.  Coal     '.  .  % 

5.  Yellow   clay    10 

6.  Blue    shale 35 

7.  Mixture   %   yellow  clay,    %   shale    . 

Table  I — Chemical  Analyses. 
Illinois  Clays  Now  Used  in  the  Manufacture  of  Paving  Brick. 


5 

> 
9 

a 
0 

c 

O 

O 

0 

2 
P 

trcT 
3 

5" 

a 

2. 

go' 
C 

5 

GO 

K—  1 

63.36 
63.35 
59  34 
60.31 
63.43 
63.62 
59.86 
64.09 
58.03 
58.52 

15.43 
16.27 
15.36 
17.74 
16.89 
16.28 
17.43 
14.16 
17.72 
15.67 

1.80 
7.56 
3.26 
5.04 
1.52 
3.02 
1.42 
2.65 
2.91 
4.99 

4.02 

"3'.84 
1.96 
4.24 
2.90 
5.10 
3.16 
5.77 
3.37 

1.58 
1.33 
1.82 
1.96 
2.11 
1.44 
2.32 
1.64 
1.43 
1.45 

.93 
1.01 

.76 

.41 
1.00 

.63 
1.05 
1.69 
1.42 
1.05 

3.28 

r-3. 

3.82 
2,88 
2.03 
2.60 
2.80 
2.90 
2.66 
2.94 

.56 
80.— 

.80 
1.07 

.20 
1.50 

.18 

.77 
1.40 
1,48 

6.99 
4.75 
7.89 
6.71 
5.97 
5.88 
6.35 
6.47 
6.47 
7.72 

.48 
.31 
.29 
.81 
.46 
.38 
.20 
.51 
.97 
2  02 

1.00 

.27 

K      2. 

K—  3 

1.31 

.84 
1.07 

.96 
1.91 

.89 
1.02 

.96 

.16 

K—  4 

.14 

K-  5 

K—  6 

.11 
.11 

K—  7 

.13 

K— 14 

.24 

K-15 

F—  1 

.25 
.32 

ROLFE] 


CLAYS    STUDIED. 
Illinois  Clays  Not  Now  Used  for  Paving  Brick. 


285 


in 

9 

> 

c 

■ad 

0 

n 

0 

0 

n 

0 

1? 
g 

5" 

3 

; 

2 

8- 

c 

H— 16 

60.93 
56.56 
39.91 
47.29 
48.41 
55.37 

17.93 
12.64 
16.43 
15.51 
18.31 
21.40 

8.12 
13.56 
4.80 
4.80 
6.06 
6.72 



.91 
2.75 
5.08 
6.19 
3  13 

.65 

1.33 
2.22 
7.57 
7.33 
5.73 
1.76 

5.01 
4.82 
3.71 
3.71 
5.65 
2.42 

5.73 
6.02 

21.02 
13.11 
12.79 
8.75 

.55 
3.70 

.86 
1.31 

.79 
3.39 

H-17 

H— 18    ....'. 

H— 20    

H— 21      

H— 23           

Clays  from  Other  States  from  Which  High  Grade  Pavers  Are  Made. 


CO 

C 

> 
0 

a 

0 

2 

0 

n 

o 

tol    p 

W5 

a 

o 

a 

o 

v> 
0 

n 

Indiana . 

K-  8 

K—  9 

K— 10    

60.89 
68.50 
58.35 
55.18 
54.37 
57.09 

58.42 
63.41 
58.57 
55.51 

55.02 
56.29 

60.31 
63.42 
56.25 
68.15 
62.70 
58.62 

16.40 
16.98 
18.09 
19.22 
23.61 
19.07 

25.05 
18.61 
20.40 
21.81 

20.35 
20.32 

19.11 
16  24 
18.79 
12.88 
16.95 
17.74 

8.20 
5.77 
6.14 
8.19 
6.14 
7.92 

3.04 
5.82 
7.40 
7.66 

6.26 
7.90 

6.14 
6.62 
8.02 
7.52 

1.61 
1.71 
2.03 
1.67 
1.61 
1.91 

1.52 
1.16 
1.37 
1.63 

1.70 
2.01 

1.73 

1.87 

1.33 

.59 

1.47 

.98 

.55 

.99 

1.20 

.56 

1.58 
.80 

.46 
.41 
.63 
.56 

.87 
.48 

2.73 
1.64 
2.39 
1.02 
1.17 
1.26 
1 

4.15 
2.97 
4.58 

2.85 
2.78 
4.69 

2.30 
3.60 
3.27 
3.56 

3.64 
4.46 

144 

4.83 
4.60 
2  93 
3. OS 
3.92 

8.18 
3.54 
7.02 
10.45 
10.09 
7.97 

8.08 
4.86 
5.95 
8.00 

9.40 
4.39 

6.70 
5.14 
7.01 
5. OS 
6.75 
6.6C 

.50 
.27 
.81 
1.02 
.60 
.43 

K-ll ~ 

K-12 

K— 13 

Ohio. 
R— 1                  

1.29 
.68 

1.06 
.02 

R— 2 

R— 3 

R— 4     

Missouri. 
S— 1 

.83 
.79 

S— 2           

Kansas. 
B— 2 

3.05 

.86 
1.49 
1.57 

.98 
2.55 
1 

G— 2      

H— 2.             

1—2 

J-2 

L-2 

8.9S 

.  8.48 

:::::::: 

Table  II — Rational  Analyses. 


Number. 


Clay 
Substance. 


Quartz. 


k-  r 

K-  3 
K-  4 
K-  5 
K—  6 
K-  7 
K-14 
K-15 
F-  1. 


38.90 
48.00 
43.32 
38.92 
41.02 
33.14 
25.28 
53.36 
51.12 


46.60 
26.74 
43.66 
46.54 
39.98 
49.36 
48.54 
22  82 
29.38 


Feldspar. 


17.50 
25.26 
13.02 
14.54 
19.  CO 
17.50 
L6.18 
23.82 
19.50 


Phos- 
phorus. 


.093 
.078 
.024 
.090 
.067 
.079 
.0(59 
.125 
.077 


Carbon. 


1.44 

1.50 
.72 

1.26 
.63 
.71 

1.01 
.90 
.92 


Soluble 
Salts. 


.13 
.14 
.04 
.08 
.38 
Tr. 
.04 
.27 
.14 


286 


PAVING    BRICK    AND    PAVING    BRICK   CLAYS. 


[BULL.    NO.    9 


Illinois  Clays  Note  Used  in  the  Manufacture  of  Pavers. 
Table  III — Physical  Tests. 


H 

3  Cfq  CD 

T  2  C 

i  fl  ai 

■»  2  — 

d  a  o 

"<  3 
1  crq 

^5 

o  o 

CO   -H 

CO 

•a 

o 
o 

3 

■d 

0 

3 

Fineness  of 

Grain. 

<: 

o 

3 
m 

ZL 
5' 

P 
crq 

r 
3' 

P 
CO 

V 

5' 
p 

crq 

a 

3 

p 

oT 

o 

ST 

CO 

EC 

crq 

o 

Number. 

I 

3 
3 

T 

3 

3 

T 

b 

3 
3 

© 

T 

8 

3 
3 

T 

© 

3 
3 

o 
0 

"2. 

o' 

p 

K—  1...   . 

7.262 
10.364 
9.004 
9.735 
5.465 
7.840 
6.435 
6.036 
5.876 
11.317 

2.66 
2.56 
2.68 
2.67 
2.65 
2.66 
2.64 
2.72 
2.65 
2.60 

26.00 
25.68 
25.56 
27.81 
25.44 
28.86 
27  90 

7.27 
1.07 
1.50 
1.40 
6  38 
1.24 
1.35 
14  23 

6.53 
1.23 
2.41 

1.74 
1.46 
1.83 
3.75 
6.31 

56.07 
66.24 
57 .  15 
48.87 
60.57 
65.83 
60.87 
42.75 

24.86 
19.63 
25.14 
29.41 
22.93 
25.98 
25.89 
26.03 

9.76 
13.90 
13.96 
22  24 
11J3 

7.77 
11.81 

9.67 

6.20 
12  20 
10.45 
10.12 

5.17 
10.06 

9.62 

6.13 

1.50 
3.47 
2.06 
3.26 
1.55 
4.10 
3.90 
1.50 

14.90 
16.77 
16.82 
16.27 
13.06 
17.03 
17.57 
13.60 
16.90 
14.60 

2  01 

K—  2 

1  62 

K—  3 

2  43 

K-  4 

K—  5 

92 

K—  6.... 

1  23 

K—  7 

1  93 

K-H 

K— 15 

2 

2 
2 

1 .  50 
<  50 

.79 

F— 1 

.00 

3.60 

2  02 

Illinois  Clays  Not  Now  Used  for  Pavers. 


1 

H 
D  crq  2 
f  2  3 

-1   ft   CO 

D  D  fC 

CO 

■a 
r» 

o 

35 

o 
o 

co_ 

Fineness  of  Grain. 

< 
o 

3* 
3 

r 

5" 
n 

pa 

p 
<7 

3 

CO 

Number. 

-5  °  2- 

3§s 

1  crq 

gs. 

3 
< 

3 
3 

T 

3 
3 

T 

b 

3 
3 

b 

T 

b 
o 

3 
3 

8 

T 

b 

3 
3 

CO 

5' 

P 

crq 

p* 

5' 
sr 
p 
crq 
re 

■a 

1 

•3 

O 
■0 

P 

H— 16 

5.670 

2.57 
2.50 
2.67 

2.72 
2.73 
2.63 

27.80 
19.00 
20.30 
23.90 
21.60 
24.90 

7.8 
21.4 

"ih'.h 

18.0 
20.4 

2.80 
7.00 
5.70 
6.80 
7.20 
7.40 

16.20 
16.60 
15.40 
18.30 
18.00 
21.40 

1.74 

H— 17    ...... 

3.70 

H-18 

H— 20 

8.117 

7.008 

8.401 

19.482 

13.05 

1.92 

.34 

1.80 

17.71 
2.75 

.80 
2.86 

27.57 
42.01 
24.34 
29.95 

26.58 
32.47 
42.77 
40.82 

19.22 
23.97 
34.62 
27.30 

2.46 

5.85 

H— 21 

3.98 

H-23 

2.05 

ROLFE] 


CLAYS   STUDIED. 


287 


Clays  from  Other  States  from  Which  High  Grade  Pavers  Are  Made. 


Number. 


R-l. 
R-2. 
K-2. 
R-4 


Ohio. 


H 

W          '"O 

•-jcrq  a 

•o         o 

ft>  3  3 

-t  n>  w 

O                O 

w  2  — 

5 

^3(J 

o            ^ 

oa" 

TO 

3^3 
•   7  d 

<5 

"< 

o  o 

Indiana. 

K-  8 

K-  9 

K-10 

K-ll 

K-12 

K-13 


Missouri. 

S-l 

S-2 

Kansas. 

B  -2 

G-2 

H-2 

1-2 

J-2 

L-2 


Fineness  of  Grain. 


5.038 

4.023 
12.503 

9.094 
22.586 

7.52H 


10.025 
8.527 
4  996 
5.032 


.071 

.SN2 


9.208 

8.634 

14.174 

13.062 

9.865 
8.526 


2.69 
2.70 
2.69 
2.66 
2.67 
2.71 


2.73 
2.64 
2.66 
2.72 


2.41 
2.60 


2.53 
2.71 
2.47 
2  67 
2.50 
2.46 


25.20 
26.12 
25.40 
22.21 
18.26 
28.30 


17.80 
24.00 
23. 
21. 


23.00 
26.40 


9.66 
11.39 
1.06 
5.36 
4.49 
1.82 


2.16 


11.69 
10.15 


26.90 
22.40 
20.70 
18.90 
24.20 
24.50 


13.17 


4.64 


6.90 

1.55 

2.42 

3.76 

2. 

1.35 


.51 


6.30 
2.84 


48.46 
65.50 
24  62 
43.74 
40.51 
46.74 


38.70 


52.90 
49.32 


2.47    52.57 


3.81    45.50    25.64 


25.40 
14.72 
44.29 
34.45 

3S.S2 
41 


39.32 


21.60 
29.13 


20.57 


10.05 
7.63 
25.52 
12.94 
15.32 
13.15 


15.53 


11.79 

10.85 


15.72 
'21*  '.40 


r 

3 

a 

P 

fB 

Vt 

s> 

*i 

ts 

3 

w 

en 

&5 

££ 

crq 

O 

rt> 

£; 

: 

<< 

7.51 
3.54 
18.29 
13.50 
12.74 
10.54 


13.9 
9.2 


5.98 


11.97 
13.1 


11.5 
7.31 
14.3 
13 

14.4 
9.7 


2.10 
.90 
5.82 
3.25 
3.60 
3.30 


4.50 
3.30 
3.00 

3.20 


14.40 
13.40 

19.  (50 
15.23 
13  35 
1(5.30 


13.40 
13.00 

13.30 
13.20 


2  70 

17.20 

4.20 

16.60 

5  00 

17.70 

1  94 

1180 

5  50 

16.50 

4  20 

14.40 

4  60 

16.50 

3.70 

16.40 

1.70 
.79 
2.31 
1.75 
5.09 
2.16 


1.95 
1.53 
1  94 

2.28 


4.76 
2.42 


1.67 
1.14 
3.07 

2.85 
2.70 
3.05 


Changes  in  Porosity  When  Fired  at  Different 

Cones. 

010  1 

08 

06 

04 

02 

1 

3 

5 

7           9 

K—  1 

36.9 
31.4 
34.5 
36.1 
32.5 
32.5 
32  2 
34.5 

34.0 
23.7 
33.2 

34.0 
33.9 
30.8 

'26.5 

34.2 

35.6 
28.0 
38.1 
34.4 

36.1 
32.9 
36.0 
36.4 
31.5 
31.9 
30.8 
31.9 

33.5 
23.8 
30.4 

34.0 
30.2 
31.3 

20.8 
s  28.3 

33.6 

36.1 
28.2 
32.  ( 
34.1 

33  1 
29.1 
31.5 
33.4 
29.9 
30.4 
27.4 
27.5 

29.7 
15.6 
22.9 

33.9 
28.3 
28.5 

25.4 

25.4 

31.7 

31.0 
27.2 
.28.3 
27.1 

29.5 
16.2 
30.7 
■28.4 
20  3 
26.2 
18.7 
24.9 

20.6 
11.3 
20.4 

31.6 
20.0 
24.6 

23.4 
18.9 

21.6 

17.5 
22.5 
21.5 
16.7 

24.7 
15.7 
24  5 
21.9 
17.7 
24.2 
20.3 
20.6 

18.1 

9.5 

20.2 

26.8 
18.5 
22.9 

21.4 
17.9 

23.9 

18.7 
18. C 
20. 1 
16. C 

28.0 
17.6 
26.1 
20.8 
15.5 
23.7 
17.3 
18.5 

18.3 
7.5 
15.7 

25  2 
17.0 
21.9 

20.7 
15.5 

17.9 

16.7 
15.6 
19.8 
15.7 

20.0 
4.5 

14  3 
7.5 
7.4 

21.6 
6.4 

10.2 

7  85 
6.00 
7.00 

22.7 
11.9 
14.3 

17.4 
11.0 

9.9 

7.4 

7.1 

16.7 

7.1 

7.40 
3.08 
6.95 
2.95 
2.28 
7.00 
1.94 
6.45 

6.9 

5.60 

2.20 

K      2 .              

3.55 

2.90 
2.62 
3.35 
2.91 

4.3 

2.45 
3.70 
3.02 

K—  3 

K—  4           

K      6.            

K    14  .               

K    15                    

F       I                       

H-16 

2.16 

H-17 

H-21 

K—  8 

13.4 
6.2 
9.5 

10.2 
4  6 

12.4 

4.8 
4.5 

7  6 
2.5 

5.4 

K— 11 

3.8 

K— 12.           

R—   1             

4.4 
1.9 

R—  2 

S—    1             

3.7 
1.4 
5.3 
1.7 

4.0 

'"i'i; 

1.6 

B-  2 

G-  2 

J-  2 

L—  2              



288 


PAVING   BRICK   AND    PAVING    BRICK   CLAYS.  [bull.  no.  9 

Changes  in  Specific  Gravity  When  Fired  at  Different  Cones. 


010 

08 

06 

04 

02 

1 

3 

5 

7 

9 

K-  1 

2.69 
2.62 
2.70 
2.07 
2.57 
2.65 
2.56 
2.65 

2.60 
2.64 
2.59 

2.70 
2.60 
2.64 

2.54 
2.61 

2.47 

2.63 
2.62 
2.56 
2.51 

2.67 
2.65 
2.70 
2.66 
2.56 
2.64 
2.54 
2. 67 

2.58 
2.61 
2.50 

2.70 
2  55 

2.68 

2.53 
2.60 

2.48 

2.68 
2.60 
2.58 
2.52 

2.68 
2.64 
2.68 
2.69 
2.55 
2.63 
2.53 
2.58 

2.58 
2.62 
2.34 

2.73 
2.59 
2.76 

2.56 
2.60 

2.50 

2.65 
2.61 
2.55 
2.49 

2.65 
2.54 
2.70 
2.70 
2.51 
2.61 
2.45 
2.64 

2.51 
2.51 
2.28 

2.72 
2.48 
2.63 

2.56 
2.56 

2.44 

2.56 
2.58 
2.53 
2.46 

2.63 
2.55 
2.69 
2.64 

2.36 
2.60 
2.56 
2.61 

2.53 
2.45 
2.33 

2.62 

"2]63 

2.57 
2.55 

2.48 

2.56 
2.51 
2.52 
2.43 

2.53 
2.56 

2.68 
2.66 

"2. 57 
2.50 
2.59 

2.49 
2.40 
2.21 

2.62 
2.49 
2.63 

2.55 
2.57 

2.41 

2.53 
2.50 
2.51 
2.48 

2.60 
2.48 

2.57 
2.47 
2.43 
2.58 
2.43 
2  47 

2.43 
1.60 
2.18 

2.57 
2.40 
2.53 

2.52 
2.46 

2.31 

2.31 
2.35 
2.47 
2.40 

2.29 
2.09 
2.41 
2.33 
2.31 
2.29 
2.19 
2.18 

2.15 

1  72 

K-  2 

K-  3 

2.19 
2.00 
2.00 
2.14 
2.00 

1.90 

1  88 

K-  4 » 

K—  6 

1.79 

K— 14 

K— 15..  . 

F-  1 

H— 16.    ...... 

2.22 

1  80 

H— 17 

H— 21 

K—  8 

2.22 
2.21 

2.41 
2.38 

2.21 
1.95 

2.35 

2.36 

2.28 

1  92 

K-ll 

K— 12 

2  21 

R—  1 

2  34 

2  07 

2.05 
2.14 
2.32 
2.29 

1.93 

1  76 

G-  2 •••  

2.21 
2.13 

L— 2 

1  96 

CONSTRUCTION  AND  CARE  OF  BRICK  PAVEMENTS.* 

[By  Iea  0.  Bakek.] 

Introduction. 

It  is  not  the  purpose  of  this  article  to  give  a  detailed  description  of 
•the  various  operations  connected  with  the  construction  of  a  brick, 
pavement,  since  those  having  the  direction  of  such  operations  are  al- 
ready familiar  with  the  work  or  can  easily  find  the  information  desired, 
•but  it  is  proposed  to  consider  some  fundamental  relations  whose  import- 
ance seems  to  have  been  overlooked  by  writers  on  the  subject  as  well  as 
by  those  having  the  construction  of  brick  pavements  in  charge.  In 
short,  this  article  is  intended  more  for  the  property  holder,  the  manu- 
facturer, and  the  layman  than  for  the  professional  engineer.  The  sub- 
jects to  be  considered  will  be  taken  up  approximately  in  the  order  in 
which  they  occur  in  the  work  of  construction. 

Historical — A  brick  pavement  consists  of  brick  set  on  edge  on  a  suit- 
able foundation — either  concrete,  gravel,  a  course  of  brick  flatwise,  or 
a  layer  of  plank.  Such  pavements  have  been  used  in  Holland  for  per- 
haps a  century,  and  to  a  much  less  extent  and  for  a  shorter  period  in 
northern  England.  Brick  pavements  were  first  used  in  the  United 
States  in  1870  at  Charlestown,  West  Virginia,  a  place  having  a  popula- 
tion of  12,000.  The  experiment  was  tried  with  a  short  section — less 
than  a  block — and  in  1873  a  block  on  the  principal  business  street  was 
laid  with  a  good  quality  of  building  brick,  and  is  still  in  service  after 
29  years.  A  block  of  brick  pavement,  laid  in  1875  on  a  leading  business 
street  of  Bloomington,  Illinois,  a  place  of  20,484  population  in  1890, 
though  constructed  of  an  inferior  building  brick  made  of  superior  clay, 
continued  in  service  for  20  years. 

At  present  brick  is  the  only  paving  material  employed  in  most  of 
the  smaller  cities  of  the  Mississippi  Valley,  and  it  is  used  extensively 
in  many  of  the  larger  cities  in  that  territory.  In  all  parts  of  this  coun- 
try, the  use  of  brick  for  residence  streets  and  light  traffic  business 
streets  is  rapidly  increasing.  A  recent  canvass  shows  about  as  much 
brick  pavement  in  progress  as  granite  block,  asphalt,  and  wood  com- 

*  Printed  by  permission  in  the  Clay  Record,  October  30,  1906. 

289 


•19  G 


290  PAVING   BEICK   AND    PAVING   BRICK   CLAYS.  [bull.  no.  9 

bined.  There  are  in  this  country  nearly  two  hundred  plants,  devoted 
to  the  manufacture  of  paving  brick,  some  having  annual  outputs  of 
60,000,000  to  100,000,000  bricks. 

Width  of  pavement — In  many  cases  a  considerable  part  of  the  money 
spent  for  a  pavement  is  wasted  by  making  the  pavement  wider  than  is 
really  necessary.  A  narrow  pavement  not  only  costs  less  to  construct, 
but  also  costs  less  to  clean  and  to  sprinkle.  Of  course,  except  for  the 
cost,  the  wider  the  pavement  the  better;  but  .length  is  more  desirable 
than  width.  An  excessive  width  is  a  needless  expense,  and  delays  or 
wholly  prevents  the  getting  of  any  pavement  at  all;  and  hence  one 
help  towards  securing  pavements  is  to  make  them  only  wide  enough  to 
accommodate  the  travel. 

It  is  not  unusual  to  find  residence  streets  in  small  cities,  without 
street  car  tracks,  with  pavements  36  to  40  feet  wide.  The  only  travel 
over  such  streets  consists  of  private  carriages  and  the  delivery  wagons 
that  supply  goods  of  various  kinds  to  the  residents.  All  the  pavement 
that  such  streets  really  require  is  a  width  such  that  two  vehicles  may 
pass  at  a  reasonable  speed  and  with  ordinary  care  without  interference. 
A  width  of  18  feet  affords  sufficient  room  for  a  vehicle  t©  pass  when 
another  is  standing  on  each  side  of  the  pavement — a  rare  occurrence ; — 
and  therefore  it  appears  that  a  pavement  18  feet  wide,  or  at  most  20 
feet,  is  sufficient  for  the  less  frequented  residence  streets.  Therefore 
any  money  spent  to  construct  a  wider  pavement  is  really  not  necessary; 
and  the  cost  of  sprinkling  and  sweeping  is  also  needlessly  increased. 
Further,  narrowing  the  pavement  increases  the  lawn  space,  which  not 
only  improves  the  appearance  of  the  street,  but  also  gives  additional 
space  in  which  to  place  gas  pipes,  water  pipes,  etc.,  and  thereby  pre- 
vents the  tearing  up  of  the  pavement  which  is  always  a  damage.  The 
only  objection  to  a  very  narrow  pavement  is  the  difficulty  of  turning 
a  team  on  it.,  The  seriousness  of  this  objection  depends  upon  the 
construction  of  the  vehicle.  Many  delivery  wagons,  express  wagons,  etc., 
may  be  turned  easily  on  an  18  foot  pavement.  If  occasionally  a  vehicle 
is  compelled  to  go  to  the  corner  to  turn,  or  even  to  drive  around  the 
block,  the  inconvenience  is  not  very  serious,  and  it  is  so  infrequent  as 
not  to  justify  any  considerable  expense  to  prevent  it.  If  the  block 
is  long,  or  if  the  objection  to  some  vehicles  being  compelled  to  drive 
around  the  block  is  considered  important,  then  it  is  much  cheaper  to 
construct  a  turning  place  near  the  center  of  the  block  than  to  build  an 
additional  e  trip  of  pavement  the  entire  length  of  the  street. 

The  cost  of  a  pavement,  per  square  yard,  is  practically  independent 
of  its  width,  and  therefore  the  reduction  of  the  width  of  the  pavement 
on  residence  streets  from  36  or  40  feet  to  18  or  20  feet  will  save  nearly 
50  per  cent  of  the  cost,  and  if  the  cost  can  be  reduced  one-half,  fne 
number  of  paved  streets  will  be  increased  much  more  than  propor- 
tionally. 

It  is  not  wise  to  take  time  to  discuss  the  width  of  pavements  on  resi- 
dence streets  containing  car  tracks,  nor  on  business  streets;  but  a  little 
investigation  will  show  that  in  many  cases  the  pavement  is  considerably 


baker]  CONSTRUCTION   OF   PAVEMENTS.  291 

wider  than  has  been  found  entirely  satisfactory  under  similar  condi- 
tions. The  views  here  express  not  more  theory,  but  are  supported  by 
experience  in  a  number  of  cities.  In  recent  years  there  has  been  a 
marked  tendency,  in  the  middle  West  a1  least,  to  reduce  the  width  of 
pavements  on  residence  streets  and  on  business  streets  in  the  smaller 
cities.  Attention  is  here  called  to  the  matter  because  far  too  often  the 
width  of  the  pavement  is  made  a  fixed  proportion  of  the  total  width 
of  the  street  regardless  of  the  real  needs  of  travel.  This  is  only  one  of 
the  many  ways  in  which  some  municipalities  suffer  from  the  lack  of 
more  eompetent  engineering  service — the  loss  frequently  being  many 
times   the  supposed  saving. 

CONSTRUCTION    OF    SUBGRADE. 

It  is  necessary  to  say  that  the  subgrade  is  the  ultimate  support  of 
any  pavement,  and  that  both  the  cost  and  the  efficiency  of  a  pavement 
depends  upon  the  supporting  power  of  the  soil  upon  which  it  rests. 
There  are'  only  two  ways  of  increasing  or  supplementing  the  supporting 
power  of  the  subgrade:  (1)  by  underdrainage,  or  (2)  by  constructing  a 
pavement  that  will  distribute  the  concentrated  load  of  the  wheel  over  a 
considerable  area  of  the  subgrade.  Usually  the  former  is  both  the 
cheaper  and  the  more  effective.  Tile  drainage  is  cheap  to  construct,  is 
certain  in  action,  and  costs  nothing  for  maintenance.  With  all  soils, 
except  clean  dry  sand,  the  cost  of  both  the  construction  and  the  main- 
tenance of  the  pavement  can  usually  be  materially  decreased  by  proper 
unclerclrainage.  Unless  the  subsoil  is  very  open  and  porous,  it  is 
economical  to  lay  a  tile  under  each  edge  of  the  pavement,  2  or  3  feet 
below  the  surface  of  the  subgrade. 

Xot  only  should  the  subgrade  be  properly  drained,  but  it  should  be 
thoroughly  rolled  to  compact  the  surface  and  also  to  reveal  any  soft 
spots.  Usually  just  before  a  pavement  is  to  be  constructed,  the  street 
is  dug  up  to  lay  sewers  and  water  and  gas  pipes  and  to  connect  these 
with  the  private  property;  and  almost  universally  the  trenches  are  re- 
filled in  such  a  manner  that  great  care  and  skill  are  required  to  con- 
struct a  pavement  which  will  not  ultimately  settle  over  the  trenches, 
much  to  the  damage  of  the  pavement  and  the  disfigurement  of  the 
street.  It  is  always  specified  that  the  subgrade  shall  be  thoroughly 
rolled ;  but  it  needs '  only  a  casual  inspection  of  the  pavements  of  any- 
city  to  show  that  this  is  seldom  in  a  manner  to  prevent  settlement.  The 
cheapest  and  surest  method  of  preventing  such  settlement  is  to  properly 
re-fill  the  trenches;  but  usually  this  is  indifferently  done,  owing  to  the 
ignorance  or  the  carelessness  of  the  proper  municipal  officer,  and  as 
a  consequence  the  remedy  of  this  defect  is  left  to  the  paving  contractor. 

The  method  to  be  employed  in  refilling  trenches  so  that  they  will  not 
settle,  depends  upon  the  kind  of  soil  and  also  upon  the  relative  cost  of 
labor  and  water.  The  problem  of  the  proper  filling  of  trenches  is  too 
intricate  to  permit  a  thorough  discussion  here ;  but  briefly  it  may  be  said 
that  except  in  the  case  of  comparatively  clean  sand  and  gravel,  back- 
filling can  be  thoroughly  done  only  by  tamping;  and  to  make  this 
method  successful  it  is  necessary   (1)   that  the  material  shall  be  moist 


292  PAVING   BRICK   AND    PAVING    BRICK   CLAYS.  [bull.  no.  9 

enough  to  be  plastic,  but  neither  too  wet  nor  too  dry,  (2)  that  it  shall 
be  deposited  in  layers  not  more  than  3  or  4  inches  thick  and  (3) 
that  each  layer  shall  be  thoroughly  tamped.  To  secure  thorough  tamp- 
ing the  relative  number  of  tampers  and  shovelers  is  sometimes  specified; 
but  this  alone  is  ineffectual  since  there  is  a  natural  tendency  for  the 
tampers  to  work  less  energetically  than  the  shovelers,  and  besides  more 
labor  is  required  to  tamp  the  soil  around  a  pipe  than  higher  up.  No 
kind  of  municipal  work  should  be  more  rigorously  inspected  than  the 
filling  of  a  trench  over  which  a  pavement  is  to  be  laid.  The  nearly 
universal  result  of  a  neglect  in  this  respect  is  that  a  pavement  built  at 
great  expense  is  disfigured  or  damaged  by  settlement,  the  repair  of 
which  will  cost  many  times  as  much  as  it  would  have  cost  to  properly 
fill  the  trench  originally. 

The  subgrade  should  be  rolled  both  longitudinally  and  transversely 
with  a  steam  roller  weighing  not  less  than  five  tons.  If  the  street  is 
rolled  in  only  one  direction,  only  one  set  of  trenches  will  be  compacted. 
The  subgrade  can  not  be  rolled  transversely  with  a  horse  roller;  and  be- 
sides the  horses'  feet  tear  up  the  subgrade  nearly  as  much  as  the  roller 
compacts  it,  particularly  when  the  rolling  is  almost  completed.  The 
roller  should  pass  over  the  surface  several  times  to  settle  the  filling  into 
the  trenches  and  also  to  compact  the  surface  by  the  kneading  action  of 
many  passes  of  the  roller.  Unfortunately  the  specification  requiring  the 
use  of  a  steam  roller  adds  somewhat  to  the  cost  of  a  pavement,  since 
that  implement  is  expensive  in  first  cost  and  also  in  maintenance;  and 
since  ordinarily  it  can  be  used  only  a  comparatively  short  time  each  year ; 
but  its  use  is  believed  to  be  worth  its  cost,  particularly  if  the  trenches 
were  not  properly  back-filled. 

FOUNDATION. 

Choice  of  Materials — There  are  several  forms  of  foundation  suitable 
for  brick  pavements,  viz. :  Concrete,  gravel,  macadam,  a  course  of  brick 
laid  flatwise,  or  a  layer  of  plank.  Concrete  is  by  far  the  most  common 
foundation;  and  apparently  a  plank  foundation  was  never  used  except 
in  a  single  city,  and  it  has  been  abandoned  there. 

It  seems  to  be  the  common  belief  that  only  a  6-inch  layer  of  concrete 
is  a  suitable  foundation  for  a  brick  pavement.  The  truth  is  that  in 
some  cases  a  6-inch  layer  of  concrete  is  unnecessarily  thick,  while  in 
other  cases  a  layer  of  gravel  or  of  broken  stone  will  make  an  equally 
good  and  more  economical  foundation.  Less  skill  is  required  with  a 
gravel  or  broken  stone  foundation  than  with  a  concrete  foundation. 
Those  who  have  made  cuts  into  concrete  pavement  foundations  report 
that  in  many  cases  the  concrete  is  no  better  than  a  layer  of  broken 
stone  without  cement,  due  apparently  to  carelessness,  or  inefficiency,  or 
dishonesty  in  the  construction.  The  process  of  placing  gravel  or  broken 
stone  is  simpler,  and  therefore  there  is  less  danger  of  inferior  work; 
and  the  gravel  or  broken  stone  requires  less  hand  labor,  which  is  an 
advantage  to  contractors  in  these  days  of  inconsiderate  demands  of 
laboring  men.     As  to  whether  concrete,  gravel,  or  broken  stone  be  used 


baker]  CONSTRUCTION   OP    PAVEMENTS.  293 

for  the  foundation  in  any  particular  case  depends  upon  local  prices  and 
the  local  condition;  and  right  here  is  where  the  city  needs  engineering 
advice  of  a  high  order,  for  a  single  word  in  the  specification  may  add 
hundreds  of  dollars  to  the  cost  of  the  work  without  any  return.  It  is 
more  scientific  and  usually  more  profitable  to  give  time  to  the  consider- 
ation of  the  specifications  beforehand  than  to  the  higgling  with  the 
contractor  afterwards. 

The  various  forms  of  foundations  will  be  considered  separately. 

Concrete — Nowadays  it  seems  to  be  the  general  belief  that  a  6-inch 
concret  base  is  necessary  for  a  brick  pavement;  at  least,  this  foundation 
is  used  indiscriminately  for  business  and  residence  streets,  and  is  used 
indiscriminately  also  on  the  stiffest  soil  and  on  the  softest.  A  6-inch 
concrete  foundation  is  ordinarily  used  under  an  asphalt  pavement,  which 
is  a  more  or  less  flexible  layer  from  2  to  3y2  inches  thick;  while  the 
same  thickness  of  concrete  is  ordinarily  used  with  a  brick  pavement 
having  a  cement  filler,  which  is  a  very  rigid  layer  from  5  to  7  inches 
thick.  Is  there  any  evidence  that  the  foundations  of  asphalt  pavements 
are  generally  too  weak? 

An  engineering  journal  recently  contained  an  account  of  a  test  of  the 
supporting  power  of  an  asphalt  pavement,  made  by  hauling  over  it  a 
truck  weighing  22,300  pounds  and  giving  a  pressure  of  slightly  over 
three  tons  on  two  wheels  having  tires  four  inches  wide.  The  founda- 
tion consisted  of  a  4-inch  layer  of  natural-cement  concrete  mixed  in 
the  proportion  of  one  part  cement,  two  parts  sand,  and  five  parts 
crushed  stone.  The  asphalt  wearing  surface  was  two  inches  thick.  The 
subgrade  consisted  of  "soft  wet  clay  which  has  been  much  disturbed  by 
many  trenches  for  sewers  and  for  water  and  gas  pipes."  The  pavement 
had  been  in  use  twelve  years  when  tested,  and  had  shown  no  signs  of 
failure.  "The  above  load  was  hauled  over  this  pavement  from  end  to 
end  and  produced  no  effect  upon  the  pavement  except  to  make  a  slight 
depression  in  the  asphalt  where  the  wheels  stood  for  half  an  hour,  the 
day  being  warm." 

Does  this  prove  that  the  concrete  foundation  of  brick  pavements  are 
generally  needlessly  thick?  Surely  if  four  inches  of  concrete  over  soft 
clay  and  under  a  2-inch  asphalt  wearing-coat  can  support  such  loads, 
six  inches  of  concrete  is  needless  under  brick  pavement  with  cement 
filler. 

Let  us  consider  this  question  from  another  point  of  view.  There 
are  three  and  only  three  reasons  for  constructing  a  pavement,  viz. : 
(1)  To  secure  a  smooth  surface  for  ease  of  cleaning  and  to  decrease 
tractive  resistance;  (2)  to  secure  an  impervious  roof  to  prevent  rain- 
water from  softening  the  subgrade;  and  (3)  to  interpose  a  layer  that' 
shall  distribute  the  concentrated  load  of  the  wheel  over  so  great  an 
area  of  the  subgrade  that  it  can  safely  support  the  load  without  depres- 
sion. For  the  moment,  we  are  not  concerned  about  the  smoothness  of 
the  surface,  and  hence  nothing  will  be  said  here  about  the  first  reason 
for  constructing  a  pavement.  The  wearing  surface  of  a  brick  pave- 
ment is  practically  impervious  whether  sand  or  cement  filler  be  used, 
and   consequently   a  concrete   foundation  is  not  necessary  to   secure   a 


294  PAVING    BRICK   AND    PAVING   BRICK   CLAYS.  [bull.  no.  9 

water-tight  roof  to  protect  the  subgrade.  Therefore,  the  concrete  foun- 
dation of. a  brick  pavement  acts  only  to  distribute  the  load  of  the  wheel 
over  the  subgrade.  The  concrete  distributes  the  load  by  virtue  of  its 
ability  to  act  as  a  beam;  and  this  property  is  due  to  the  cement  whicl* 
the  concrete  contains.  If  there  were  no  cement  in  the  concrete,  the  layer 
of  gravel  or  crushed  stone  would  distribute  the  concentrated  load  of  the 
wheel  over  a  considerable  area.  The  pressure  of  the  wheel  is  transmitted 
downward  in  diverging  lines;  and  if  the  point  of  contact  of  the  wheel 
is  considered  as  the  apex  of  a  cone  having  its  base  on  the  subgrade,  it 
may  be  assumed  that  the  load  of  the  wheel  distributed  nearly  uniformly 
over  the  base  of  this  cone.  It  is  unwise  to  attempt  here  to  go  into  the 
mathematics  of  the  subject  further,  but  the  efficiency  of  a  layer  of 
broken  stone  in  distributing  a  concentrated  load  is  proved  by  the 
fact,  that,  under  favorable  circumstances  as  to  soil  and  drainage,  4 
inches  of  broken  stone  has  successfully  carried  considerable  travel, 
while  6  inch  macadam  roads  are  quite  common  in  a  number  of  states. 
If  4  or  6  inches  of  macadam  without  any  other  pavement  will  carry 
travel,  the  same  thickness  will  certainly  make  a  good  foundation  for  a 
brick  pavement  under  ordinary  conditions — particularly  if  a  cement 
filler  is  used,  since  the  filler  gives  the  course  of  brick  a  considerable 
transverse  strength,  as  will  be  discussed  later.  The  writer  recently 
saw  a  piece  of  brick  pavement  with  sand  filler  which  is  laid  directly 
upon  the  black  loam  of  the  Illinois  corn  belt,  which  for  six  or  eight 
years  has  carried  the  heaviest  travel  of  a  city  of  three  or  four  thousand 
inhabitants,  and  which  is  still  in  good  condition.  A  tile  drain  was  laid 
at  each  side  of  the  street,  the  subgrade  was  well  rolled,  and  the  paving 
bricks  (not  blocks)  were  .laid  upon  a  layer  of  sand  and  small  gravel 
only  one  or  two  inches  thick.  Probably  no  small  part  of  the  success 
of  this  pavement  is  due  to  the  fact  that  a  prominent  intelligent  and 
successful  local  business  man  acted  as  inspector.  The  writer  does  not 
advocate  the  general  adoption  of  this  form  of  construction;  but  cites 
this  case  to  show  what  can  be  done  by  intelligence  and  care,  and  to  prove 
that  a  layer  of  concrete  is  not  always  necessary.  A  needlessly  expen- 
sive form  of  construction  is  not  only  money  wasted,  but  deters  the  con- 
struction of  other  pvaements. 

Not  infrequently  pavements  having  a  concrete  foundation  are  found 
which  have  settled  over  trenches.  Does  not  this  prove  that  the  ordinary 
concrete  foundation  is  not  strong  enough?  No,  it  simply  proves  that 
the  foundation  over  the  trench  was  not  strong  enough.  There  are  two 
remedies  for  this  condition  of  affairs.  Either  consolidate  the  filing  in 
the  trench  better  by  rolling  or  tamping  as  described  above,  or  make  the 
concrete  thicker  over  the  trench.  The  first  is  cheaper  and  more  scien- 
tific. In  no  case  is  it  justifiable  to  thicken  or  strengthen  the  founda- 
tion over  the  entire  street  simply  because  trenches  occupying  from  5 
to  10  per  cent  of  its  surface  may  not  have  been  properly  back-filled. 

Before  considering  substitutes  for  concrete  foundations,  let  us  exam- 
ine the  concrete  a  little  further.  Formerly  it  was  the  custom  to  use  a 
rich  natural-cement  concrete,  because  it  was  cheaper  than  a  Portland- 


baker]  CONSTRUCTION    OF    PAVEMENTS.  295 

cement  concrete  of  equal  strength.  A  few  years  ago  nearly  all  the 
Portland  cement  used  in  the  country  was  imported,  while  now  nearly 
all  of  it  is  of  domestic  manufacture;  and  further,  it  is  not  only  home- 
made, but  is  both  better  and  cheaper.  Although  natural  cement  is 
marvelously  cheap,  a  concrete  of  a  given  strength  can  be  made  cheaper 
of  Portland  than  of  natural  cement.  Experiments  made  at  the  Uni- 
versity of  Illinois  show  that  a  concrete  composed  of  one  part  cement, 
eight  parts  of  coarse  sand  or  fine  gravel,  and  eight  parts  of  screened 
or  broken  stone  was  considerably  stronger  in  compression  and  also  in 
bending  than  a  concrete  composed  of  one  part  natural  cement,  three 
parts  of  the  same  sand,  and  three  parts  of  the  same  broken  stone. 
These  proportions  have  been  practically  tested  in  the  construction  of 
half  a  mile  of  pavement  with  the  greatest  satisfaction  to  all  parties 
concered.  Prices  vary  greatly  with  the  locality,  but  in  most,  if  not  all, 
cases  Portland-cement  concrete  is  cheaper  in  proportion  to  strength 
than  that  made  with,  natural  cement. 

Before  dropping  the  subject  of  concrete  foundations,  a  few  words 
should  be  said  in  condemnation  of  the  quite  general  practice  of  leaving 
the  upper  face  of  the  concrete  needlessly  rough  and  irregular,  with  loose 
stones  strewn  over  the  surface.  To  secure  a  uniform  surface  for  the 
pavement,  the  cushion  coat  should  be  of  uniform  thickness,  and  hence 
the  top  face  of  the  concrete  should  be  practically  -parallel  with  the  sur- 
face of  the  finished  pavement.  Also  any  loose  stones  on  top  of  the 
concrete  causes  the  brick  to  be  broken  during  the  rolling  and  produces 
inequalities  in  the  surface  of  the  finished  pavement.  Both  of  these 
effects  can  be  eliminated  without  appreciable  expense  "by  a  little  care. 

Gravel — AVhere  gravel  is  cheap,  it  is  better  to  use  a  thicker  layer  of 
gravel  without  cement  than  a  6  inch  layer  of  gravel  with  cement,  i.  e., 
a  6  inch  layer  of  concrete.  To  secure  a  good  foundation,  the  gravel 
must  be  properly  used,  which  apparently  is  seldom  or  never  done. 
The  usual  method  seems  to  be  to  dump  the  gravel  upon  the  subgrade 
directly  froin  wagons,  and  then  to  level  off  between  the  piles  with 
shovels.  By  this  process  the  lower  part  of  the  original  piles  is  much 
more  compact  than  the  space  between  the  piles;  and  rolling  does  not 
materially  lessen  the  inequalities,-  since  the  roller,  being  a  cylinder  of 
considerable  length,  rides  upon  the  tops  of  the  piles  and  does  not  com- 
press the  gravel  between  them.  The  result  is  that  soon  after  the  pave- 
ment is  completed,  the  natural  settlement  of  the  gravel  foundation 
causes  the  surface  to  be  full  of  depressions. 

The  better  and  cheaper  method  is  to  level  off  the  piles  with  a  scrap- 
ing roacl-grader,  (the  ordinary  "road  machine")  and  then  thoroughly 
harrow  the  gravel  with  a  long-toothed  harrow,  after  which  the  founda- 
tion should  be  rolled.  For  the  best  results,  the  gravel  should  be  spread 
in  layers  not  more  than  three  or  four  inches  thick.  Brick  pavements 
upon  gravel  foundations  laid  by  this  method  have  shown  no  depressions 
after  many  years,  while  those  constructed  with  the  utmost  care  by  the 
preceding  method  with  the  same  gravel  on  the  same  soil  have  been 


2^>6  PAVING   BRICK   AND    PAVING   BRICK   CLAYS.  [bull.  no.  9 

full  of  holes.  This  is  another  example  showing  that  cheaper  materials 
and  proper  methods  intelligently  give  better  results  than  expensive 
materials  improperly  used. 

Broken-stone — Where  broken  stone  is  cheap,  it  is  better  economy  to 
use  more  stone  and  omit  the  cement  from  the  foundation,  i.  e.,  use 
broken  stone  alone  instead  of  concrete.  If  the  rock  is  soft  or  contains 
much  fine  material  as  it  comes  from  the  crusher,  it  should  be  screened 
to  take  out  all  dust  and  most  of  the  pieces  up  to  say  14  inch  in  greatest 
dimensions.  The  broken  stone  may  be  hauled  to  the  street  in  wagons, 
and  dumped  upon  the  subgrade.  It  may  be  spread  by  hand  with  forks 
or  rakes,  or  it  may  be  spread  with  a  scraping  road-grader,  the  latter 
method  being  the  cheaper.  In  spreading  the  stone  care  should  be 
taken  that  the  several  sizes  are  not  separated  too  much,  and  that  the 
piles  on  which  the  stone  was  dumped  from  the  wagons  are  not  left 
too  high.  The  layer  of  stone  should  be  rolled  until  the  individual 
stones  do  not  move  as  one  walks  over  the  surface,  or  until  the  surface 
stones  are  not  easily  kicked  out  with  the  foot.  After  the  completion  of 
the  rolling,  the  surface  of  the  broken  stone  should  be  impervious  to  the 
sand  to  be  used  in  the  cushion  coat.  With  most  stone  this  condition 
will  be  secured  by  the  crushing  of  the  top  layer  of  the  broken  stone 
during  the  rolling;  -but  if  there  are  spots  that  are  porous,  throw  on  a 
few  shovelfuls  of  fine  stone  and  roll  again.  If  the  stone  is  hard,  it 
may  be  necessary  after  the  rolling  is  nearly  completed  to  apply  a  thin 
coat  of  finer  or  softer  stone.  Of  course  the  top  of  the  foundation  should 
finally  be  left  smooth  and  of  proper  grade  and  crown. 

The  rolling  required  with  either  a  gravel  or  broken-stone  founda- 
tion can  best  be  done  with  a  steam  roller,  which  is  only  an  additional 
reason  for  specifying  that  the  subgrade  shall  be  rolled  with  a  steam 
roller.  Although  it  is  a  little  out  of  place  here,  this  is  the  most  con- 
venient place  to  say  that  a  steam  roller  is  also  much  better  than  a  horse 
roller  for  rolling  the  brick.  If  the  subgrade,  and  the  gravel  or  broken- 
stone  foundation,  and  the  brick  are  all  rolled  with  a  steam  roller,  the 
cost  of  rolling  any  one  of  these  is  materially  lessened,  since  the  roller  is 
thus  used  a  greater  part  of  the  time. 

Brick — The  first  brick  pavements  were  laid  on  a  foundation  consist- 
ing of  a  layer  of  gravel  and  a  course  of  brick  laid  flatwise.  This  form 
of  foundation  has  been  abandoned  for  two  reasons:  first,  because  some 
other  form  is  usually  cheaper;  and  second,  because  of  the  lack  in  the 
past  of  proper  precautions  in  laying  this  form  of  foundation.  There 
have  been  two  defects  in  constructing  this  form  of  foundation.  First, 
the  gravel  is  neither  spread  nor  consolidated  uniformly.  The  proper 
method  of  spreading  and  rolling  the  gravel  has  been  described  above 
under  the  head  Gravel.  The  second  defect  consists  in  laying  broken 
bricks  with  their  broadest  side  up,  and  hence  the  space  below  is  not 
well  filled  while  the  cushion  coat  is  being  spread,  and  consequently 
after  the  pavement  is  completed  the  cushion  coat  works  into  these 
cavities  and  permits  the  surface  of  the  pavement  to  sink.  If  all  broken 
brick  are  laid  on  the  broad  side  and  care  be  taken  thoroughly  to  fill 
the  joints  while  laying  the  cushion  coat,  this  form  of  foundation  will 


baker]  CONSTRUCTION   OF    PAVEMENTS.  297 

give  satisfaction,  even  though  the  lower  course  of  brick  be  quite  in- 
ferior. The  writer  is  quite  familiar  with  a  piece  of  such  pavement  laid 
on  a  very  unfavorable  subgrade,  but  with  proper  precautions  in  the  two 
respects  mentioned  above,  which  for  ten  or  fifteen  years  has  given  entire 
satisfaction  and  has  as  good  a  surface  as  adjoining  pavements  on  a  con- 
crete base,  even  though  the  latter  are  on  a  more  favorable  subgrade  and 
carry  less  travel.  This  pavement  illustrates  a  rule  of  construction 
that  can  not  be  repeated  too  often,  viz. :  No  good  brick  pavement  can 
be  constructed  without  proper  attention  to  all  details. 

CUSHION. 

The  cushion  is  a  layer  of  sand  1  to  2  inches  thick  between  the  founda- 
tion and  the  wearing'  course  of  brick,  to  secure  a  uniform  bed  or  bearing 
for  the  brick.  Unless  the  bricks  or  blocks  are  unusually  uniform,  the 
cushion  layer  should  be  2  inches  thick. 

The  thickness  should  be  as  uniform  as  possible  so  that  the  bricks  will 
settle  evenly  during  the  rolling;  and  therefore  the  top  of  the  concrete 
foundation  should  be  carefully  finished  with  a  surface  parallel  to  the 
surface  of  the  pavement.  Not  infrequently  loose  fragments  of  stone 
are  left  on  the  surface  of  the  concrete,  a  result  which  is  very  undesirable, 
since  they  necessitate  a  thicker  cushion  and  at  best  prevent  the  bricks 
from  coming  to  a  uniform  bearing.  With  good  workmanship  in  laying 
the  concrete,  there  will  be  no  loose  pieces  of  stone  on  the  surface;  and 
if  they  do  happen  to  get  there,  they  should  be  removed  before  laying 
the  cushion  coat. 

When  the  sand  cushion  is  laid  on  a  foundation  of  broken  stone,  care 
must  be  taken  to  roll  the  stone  so  that  the  jar  of  the  traffic  will  not 
cause  the  sand  to  work  into  the  broken  stone,  thus  permitting  the  pave- 
ment to  settle  and  to  become  rough  and  uneven.  If  the  broken  stone  is 
rolled  until  the  surface  of  the  layer  is  firm  and  solid  and  does  not  shake 
under  the  foot  in  walking  over  it,  unless  the  stone  is  very  hard  and 
tough  there  is  not  much  danger  of  the  sand's  sifting  into  the  stone. 

The  sand  for  the  cushion  should  preferably  be  so  fine  as  to  be  of  a 
soft,  velvety  nature,  and  should  contain  no  pebbles  of  any  considerable 
size,  or  loam  or  vegetable  matter.  The  size  of  pebbles  permissible  de- 
pends upon  the  thickness  of  the  sand  bed.  Pebbles  will  prevent  the 
brick  from  having  a  uniform  bearing;  the  loam  is  likely  to  be  washed 
to  the  bottom  of  the  layer  and  cause  the  brick  to  settle ;  while  the  vege- 
table matter  will  decay  or  wash  away,  and  leave  the  brick  unsupported. 

The  spreading  of  the  sand  should  be  carefully  done,  so  as  to  secure 
a  uniform  thickness  and  to  have  its  upper  surface  exactly  parallel  to 
the  top  of  the  finished  pavement.  After  the  sand  has  been  distributed 
approximately  to  the  proper  thickness  with  a  shovel,  the  surface  should 
be  leveled  by  drawing  over  it  a  template  conforming  exactly  to  the 
curvature  of  the  cross-section  of  the  proposed  surface  of  the  pavement. 
The  template  should  be  drawn  slowly  over  the  sand  bed  several  times, 
any  depressions  that  develop  being  filled  by  sprinkling  sand  into  them 
with  a  shovel.     A  considerable  quantity  of  sand  should  be  drawn  along 


^98  PAVING    BRICK    AND    PAVING    BRICK   CLAYS.  [bull.  no.  9 

in  front  of  the  template,  as  this  aids  materially  in  packing  the  bed. 
It  is  necessary  to  draw  the  template  several  times  to  pack  the  sand  well, 
particularly  if  there  are  wet  and  dry  spots,  as  the  successive  jarring  of 
the  sand  grains  causes  them  to  settle  more  closely  together.  When  the 
sand  cushion  is  properly  packed  it  will  have  a  uniform,  smooth,  velvety 
appearance,  and  will  not  look  rough,  porous  and  grainy. 

The  surface  of  the  cushion  layer  is  often  prepared  with  a  short  lute; 
but  the  template  secures  a  more  uniform  surface  and  also  gives  a  greater 
compression  and  more  even  bed.  With  hand  luting  the  surface  ^of  the 
pavement  is  almost  certain  to  be  covered  with  saucer-like  depressions 
after  it  has  been  rolled.  Hand  luting  should  be  prohibited  except 
where  the  use  of  the  template  is  impossible,  as  around  man-hole  covers, 
at  street  intersections,  etc. 

THE  BRICK. 

Character — A  paving  brick  is  simply  a  brick  which,  owing  to  careful 
selection  of  the  clay  and  to  skill  in  the  manufacture,  is  so  hard  and 
tough  that  it  will  resist  the  crushing  and  the  abrading  action  of  the 
traffic.  The  brick  should  be  reasonably  perfect  in  shape,  should  be  free 
from  marked  warping  or  distortion,  and  should  also  be  uniform  in  size, 
so  as  to  fit  closely  together  and  make  a  smooth  pavement.  Any  par- 
ticular brick  should  be  homogeneous  in  texture  and  should  be  free  from 
lamination  or  seams,  so  as  to  wear  uniformly;  and  all  the  brick  used  in 
a  pavement  should  be  of  the  same  grade  so  that  the  pavement  may  wear 
evenly. 

Testing — To  determine  the  difference  in  quality  of  bricks  of  different 
manufacture,  it  is  necessary  to  carefully  test  them.  This  is  done  by 
rolling  the  bricks  or  blocks  with  blocks  of  cast-iron  in  a  revolving  cast- 
iron  cylinder  or  "rattler."  The  National  Brick  Manufacturer's  Asso- 
ciation, as  a  result  of  an  extended  series  of  experiments,  has  adopted  a 
standard  method  of  conducting  this  test  which  is  so  well  known  or  so 
easily  obtained  as  to  make  it  unwise  to  give  the  details  here. 

Different  bricks  are  rated  according  to  the  loss  by  wear  in  the 
"rattler;"  but  the  per  cent  of  loss  will  depend  upon  the  care  employed 
in  culling  the  brick  and  in  selecting  the  samples,  as  well  as  upon  the 
character  of  the  brick.  To  show  the  results  that  may  be  expected,  the 
following  data  obtained  by  a  city  in  Illinois  in  the  ordinary  course  of 
business  are  given.  The  samples  were  selected  after  delivery  upon 'the 
the  street,  by  a  representative  of  the  city.  The  test's  were  carefully 
made  according  to  the  "N.  B.  M.  A.  standard"  as  above.  The  material 
was  in  the  form  of  books  approximately  3"  x  "  9".  The  average  loss  of 
ten  lots  was  18.34  per  cent  with  a  range  from  15.4.  to  24.6  per  cent; 
and  omitting  the  largest  result,  the  average  was  17.64  per  cent  with  a 
range  from  15.4  to  21.2  per  cent.  Of  the  ten  kinds  of  blocks,  two  had 
losses  of  less  than  16  per  cent,  four  less  than  18,  six  less  than  19,  and 
eight  less  than  20  per  cent. 


bakerJ  CONSTRUCTION    OF    PAVEMENTS.  299 

The  above  data  arc  for  blocks  approximately  3"x4"x9".  Bricks 
approximately  2"x4"x8"  will  lose  from  2  to  G  per  cent  more  than 
the  above  blocks;  but  not  enough  data  have  been  accumulated  to  deter- 
mine with  any  accuracy  the  effect  of  size  upon  the  loss  in  the  rattler 
best. 

A  study  of  the  details  of  the  experiments  referred  to  above  indicate- 
that  an  occasional  manufacturer  can  furnish  paving  blocks  giving  a  loss 
of  15  per  cent  or  even  less;  but  whether  it  is  wise  so  to  specify  will  de- 
pend upon  the  service  required  and  upon  the  cost  of  different  grades 
of  paving  blocks.  A  severe  specification  will  require  more  careful 
culling  of  the  product  of  the  kiln  and  will  also  limit  competition — both 
of  which  demands  will  increase  the  cost.  The  limit  to  be  specified  in 
any  particular  case  will  depend  upon  the  special  conditions;  and  should 
lie  the  result  of  very  careful  study  of  the  attendant  conditions. 

Set  line/  the  Brick — There  is  neither  space  nor  need  of  discussing  this 
subject  here,  further  than  to  say  that  each  brick  should  be  pressed  or 
rather  struck  against  the  side  and  also  the  end  of  the  bricks  already 
in  position. 

Inspection — After  the  bricks  have  been  set  in  position  the  pavement 
should  be  carefully  inspected,  and  all  very  soft  or  very  hard  bricks 
should  be  removed  so  that  the  pavement  may  wear  uniformly.  A  brick 
having  only  a  small  piece  chipped  from  the  corner  or  edge  may  be  turned 
over. 

ROLLING  THE  PAVEMENT 

After  all  rejected  brick  have  been  removed  and  the  pavement  has  been 
swept,  it  is  ready  for  rolling,  which  should  be  done  with  a.  steam  roller 
weighing  from  3  to  6  tons.  A  very  heavy  roller  is  undesirable,  at  least 
in  the  beginning  of  the  rolling,  since  the  first  passage  of  it  tilts  the  brick 
to  one  side  so  much  that  it  is  nearly  impossible  to  straighten  them  up 
again.  The  roller  should  not  weigh  more  than  six  tons,  and  four  is 
better.  Unless  the  top  faces  of  the  bricks  are  brought  to  a  plane,  the 
pavement  will  be  rough  and  noisy,  and  will  lack  durability.  The  bricks 
should  be  firmly  settled  into  the  sand  bed  so  that  traffic  may  not  de- 
press some  of  the  brick,  which  will  make  the  pavement  rough  and  also 
make  it  wear  needlessly  fast. 

The  pavement  should  first  be  rolled  longitudinally,  beginning  at  the 
crown  and  working  toward  the  gutter,  taking  care  that  each  return 
trip  of  the  roller  covers  exactly  the  same  area  as  the  preceding  trip  so 
that  the  second  passage  of  the  roller  may  neutralize  any  careening  of  the 
brick  due  to  the  first  passage.  Pavements  that  have  been  rolled  only  once 
or  always  in  one  direction  are  very  much  rougher  and  more  noisy  than 
when  properly  rolled.  If  a  spot  is  skipped  on  the  return  passage  of 
the  roller,  it  can  be  detected  by  a  casual  inspection  of  by  the  noise  of  a 
passing  vehicle.  The  first  passage  of  the  roller  should  be  made  at  a 
slow  speed,  not  faster  than  a  slow  walk,  to  prevent  undue  canting  of 
the  brick.  After  the  pavement  has  been  rolled  longitudinally,  roll  it 
back  and  forth  transverselv,  or  at  least  in  both  directions  at  an  angle  of 


300  PAVING   BRICK    AND    PAVING   BRICK   CLAYS.  [bull.  no.  9 

45  degrees  from  curb  to  curb.  The  purpose  of  the  rolling  is  to  settle 
the  bricks  uniformly  into  the  cushion  layer  or  sand  bed.  The  rolling 
should  not  be  done  with  a  horse  roller,  since  the  horse's  feet  disturb  the 
position  of  the  loose  brick,  and  also  it  is  impossible  to  roll  the  street 
transversely. 

PILLING  THE  JOINTS. 

The  joints  between  the  bricks  or  blocks  should  be  filled  to  keep  the 
brick  in  the  proper  position,  to  lessen  the  chipping  of  the  edges  of  the 
brick,  and  to  prevent  water  from  penetrating  to  the  cushion  coat  and  to 
the  foundation.  Three  forms  of  filler  are  in  common  use,  viz. :  Sand, 
tar  and  hydraulic  cement. 

Sand  Filler — Sand  was  the  first  filler  employed  for  brick  pavements, 
and  in  the  Middle  West  is  even  yet  almost  exclusively  used.  The  sand 
should  be  fine  and  dry,  and  should  be  worked  into  the  joints  by  sweep- 
ing it  over  the  pavement,  which  also  should  be  dry.  Although  the 
sand  is  nominally  always  swept  into  the  joints,  it  is  usually  simply 
spread  upon  the  surface  and  left  to  be  worked  in  by  traffic,  which  is  un- 
desirable since  the  joints  are  eventually  filled  with  manure  and  street 
dirt.  The  sand  can  be  swept  into  the  joints  effectively  and  economically 
with  a  revolving  machine  sweeper.  The  cost  of  sweeping  the  pavement 
preparatory  to  filling  the  joints  and  the  filling  of  the  joints,  including 
the  cost  of  sand,  is  usually  about  two  cents  per  square  yard. 

The  advantages  of  a  sand  filler  are:  1.  It  is  cheaper  than  any  other 
form  of  filler.  2.  The  pavement  may  be  thrown  open  to  traffic  as 
soon  as  the  bricks  are  laid.  3.  The  pavement  may  be  taken  up  easily 
and  without  breakage  of  the  brick.  4.  It  is  practically  watertight, 
particularly  after  being  in  service  a  short  time. 

The  disadvantages  of  a  sand  filler  are:  1.  It  does  not  protect  the 
edges  of  the  brick  from  chipping.  2.  It  may  be  washed  out  on  steep 
slopes.  3.  It  is  removed  from  the  top  of  the  joints  by  the  street 
sweeper. 

Tar  Filler — Tar  is  occasionally  used  as  a  filler  for  the  joints  of  a 
brick  pavement  pavement.  The  grade  ordinarily  used  is  that  known 
to  the  trade  as  No.  5  or  No.  6  coal-tar  distillate.  The  bricks  should  be 
dry,  and  the  tar  should  be  applied  at  a  temperature  of  300°  to  320° 
Fahr.  by  being  poured  into  the  joints  with  a  vessel  very  much  like  a 
sprinkling  pot  without  the  nose.  The  success  or  failure  of  the  tar 
filling  depends  on  the  efficiency  and  care  of  the  person  in  charge  of 
heating  the  tar.  If  the  tar  be  too  hard,  it  pulverizes  in  very  cold  weather ; 
if  it  be  too  soft,  it  runs  and  becomes  sticky  in  very  hot  weather.  The 
cost  of  a  tar  filler  depends  upon  the  locality  and  upon  the  closeness  of 
the  joints.  Usually  tar  costs  from  6  to  8  cents  a  gallon;  and  one 
gallon  is  generally  sufficient  for  one  square  yard  of  pavement.  The 
total  cost  of  the  filler  varies  .from  10  to  12  cents  per  square  yard  of 
pavement. 


baker]  CONSTRUCTION  OF  PAVEMENTS.  301 

Tar  is  superior  to  sand  in  that  it  makes  a  perfectly  watertight  joint; 
and  it  is  superior  to  hydraulic-cement  grout  in  that  it  is  not  so  rigid 
and  therefore  makes  a  more  quiet  pavement.  Tar  costs  more  than  sand, 
and  does  not  protect  the  edges  of  the  brick  as  well  as  hydraulic-cement 
grout. 

The  objections  to  tar  are:  1.  In  summer  it  is  likely  to  melt  and  run 
out  of  the  joints;  and  in  winter  it  is  brittle  and  likely  to  chip  out  of 
the  joints.  2.  The  heating  of  it  makes  unpleasant  odors  on  the 
street. 

Cement  filler — The  most  common  joint  filler,  other  than  sand,  is  a 
thin  mortar  composed  either  of  neat  Portland  cement  or  of  1  part 
cement  and  1  part  fine  sand,  the  latter  proportions  being  the  more 
common.  The  pavement  should  be  copiously  sprinkled  immediately 
before  the  grout  is  applied.  The  sand  and  the  cement  should  be  mixed 
in  batches  say  of  not  more  than  40  to  50  pounds  of  each  at  one  time, 
in  a  tight  mortar  box.  The  box  for  this  purpose  should  be  3 y2  to 
4  feet  long,  27  to  30  inches  wide,  and  12  to  14  inches  deep,  and  should 
have  legs  of  different  lengths,  so  that  the  mixture  will  readily  flow 
to  the  lower  edge  of  the  box,  which  should  be  8  to  10  inches  above  the 
pavement. 

The  sand  and  the  cement  should  first  be  mixed  dry ;  and  when  the  dry 
mixture  assumes  an  even  and  unbroken  shade,  water  should  be  added 
in  a  sufficient  quantity  to  form  a  grout  of  the  consistency  of  thin 
cream.  The  grout  should  be  removed  from  the  box  to  the  pavement 
with  a  scoop  shovel,  and  not  by  overturning  the  box;  since  by  the  last 
process  the  sand,  cement,  and  water  are  separated  and  are  deposited  on 
different  portions  of  the  pavement.  While  the  box  is  being  emptied  the 
grout  should  be  constantly  stirred  to  prevent  a  separation  of  the  sand 
from  the  cement;  and  after  the  grout  has  been  applied  to  the  pavement, 
it  should  be  quickly  swept  into  the  joints  with  steel  brooms.  It  is  better 
that  the  joints  should  be  only  about  half  filled  at  the  first  application, 
since  then  there  is  a  less  depth  of  grout  in  the  joints  and  consequently 
less  liability  of  the  separation  of  the  sand,  the  cement,  and  the  water. 

To  secure  the  best  results,  a  mortar  box  should  be  provided  for  each 
10  feet  of  width  of  the  street,  and  the  full  width  of  the  street  should 
be  filled  at  practically  the  same  time.  After  the  filling  has  been  carried 
forward  for  40  or  50  feet,  the  same  space  should  be  filled  again  in  like 
manner,  except  that  the  mixture  for  the  second  filling  should  be  slightly 
thicker  than  the  first.  The  joints  should  be  filled  entirely  to  the  top 
in  the  second  application.  After  the  joints  have  thus  been  filled,  a  half 
inch  of  fine  sand  should  be  spread  over  the  entire  surface  of  the  pave- 
ment ;  and  if  the  weather  is  very  hot  or  dry,  the  sand  should  be  sprinkled 
at  intervals  for  two  or  three  days,  to  insure  that  the  cement  does  not 
lose  by  vaporation  the  water  necessary  for  chemical  combination  in 
setting.  Traffic  should  be  kept  off  the  pavement  from  7  to  10  days,  or 
at  least  until  the  cement  has  firmly  set.  If  the  cement  filler  is  dis- 
turbed before  it  is  fully  set,  it  is  practically  no  better  than  sand.     If 


302  PAVING    RRICK    AND    PAVING   BRICK   CLAYS  [bull.  no.  9 

the  cement  filler  is  put  in  as  described  above  and  allowed  to  set  firmly 
before  being  used,  it  will  wear  no  faster  than  the  best  paving  bricks  and 
will  prevent  spalling  and  chipping  of  the  bricks  at  the  edges  and 
corners. 

The  amount  of  grout  required  will  vary  with  the  openness  of  the 
joints,  with  the  depth  of  the  grooves,  and  also  with  the  quantity  of 
sand  of  the  cushion  coat  that  works  up  into  the  lower  part  of  the 
joints,  while  the  bricks  are  being  rolled.  With  a  grout  mixed  1  to  1, 
a  barrel  of  cement  will  usually  fill  from  25  to  40  square  yards.  The  cost 
of  mixing  the  grout  in  small  quantities  and  applying  it  as  above  varies 
from  1  to  114  cents  per  square  yard;  and  with  ordinary  re-pressecl 
blocks  and  reasonable  care  in  securing  close  joints,  the  cost  of  a  1  to  1 
Portland-cement  grout  applied  as  described  above  will  usually  vary 
from  10  to  12  cents  per  square  yard. 

The  advantage  of  the  cement  filler  is  that  it  protects  the  edges  of 
the  bricks  from  chipping,  and  thus  adds  to  the  durability  of  the  pave- 
ment. When  the  joints  are  filled  with  sand  or  tar,  the  edges  of  the 
bricks  chip  off,  the  upper  faces  wear  round,  the  pavement  becomes 
rough,  and  the  impact  of  the  wheels  in  jolting  over  the  surface  tends 
to  destroy  the  brick ;  while  with  a  good  cement  filler,  the  edges  do  not 
chip,  the  whole  surface  of  the  pavement  is  a  smooth  mosiac  over  which 
the  wheels  roll  without  jolt  or  par,  and  consequently  the  life  of  the 
pavement  is  materially  increased. 

An  objection  to  the  cement  filler  is  that  it  does  not  take  up  the  ex- 
pansion of  the  pavement  due  to  increase  of  temperature,  and  that  con- 
sequently the  pavement  is  likely  to  rise  from  the  foundation  and  give 
out  a  rumbling  noise  as  vehicles  go  over  it.  This  rumbling  can  be  pre* 
vented  by  placing  a  tar- joint  from  %■  to  1  inch  thick  next  to  each 
curb.  The  compression  of  the  tar  allows  the  bricks  to  expand  without 
lifting  the  pavement  from  its  foundation.  This  tar-joint  can  be  inserted 
by  setting  a  1  inch  board  next  to  the  curb  before  laying  the  bricks,  and 
then  after  the  bricks  are  laid  withdrawing  it  and  filling  the  space  with 
coal-tar  distillate  No.  5  or  6.  The  longitudinal  expansion  can  be  taken 
up  either  by  filling  three  or  four  transverse  joints  with  tar,  each  25  or 
30  feet,  or  by  inserting  a  1  inch  tar-joint  each  40  or  50  feet.  These 
expansion  joints  will  require  a  gallon  of  tar  for  each  5  or  6  square 
yards. 

An  alleged  objection  to  the  cement  filler  is  that  in  making  repairs 
it  is  difficult  to  remove  the  brick  without  breaking  many,  and  it.  is 
difficult  to  clean  brick  so  that  they  may  be  used  again.  This  is  really 
an  advantage  if  it  will  in  any  degree  prevent  the  tearing  up  of  the 
pavement;  and  at  best  this  objection  ought  not  to  have  much  weight 
against  durable  construction. 

A  third  objection  is  that  the  street  can  not  be  used  while  the  cement 
is  setting.  Often  the  cement  is  not  allowed  to  set  fully  before  throw- 
ing the  street  open  to  travel,  and  consequently  the  chief  advantage  of 
the  rigid  filler  is  lost. 


baker]  CONSTRUCTION   OF    PAVEMENTS.  303 

MERITS   OF   BRICK   PAVEMENTS. 

Bricks  as  paving  material  have  some  attractive  features. 

1.  They  may  be  had  in  small  units  of  practically  uniform  size. 
2.  They  may  be  had  in  large  or  small  quantities.  3.  They  may  be 
laid  rapidly  without  special  expert  labor.  4.  When  failing  pipes  or 
other  causes  necessitate  the  disturbance  of  the  pavement,  ordinary  tools 
and  intelligence  can  restore  the  original  surface.  5.  Brick  pavements 
give  a  good  foothold  for  horse.  6.  They  do  no  wear  slippery.  7. 
They  are  adapted  to  all  grades,  being  used  upon  grades  of  10  to  15  per 
cent  without  serious  accident  or  inconvenience.  8.  They  have  low 
tractive  resistance,  particularly  if  the  joints  are  filled  with  Portland 
cement  grout.  9.  They  are  not  specially  noisy  when  properly  laid. 
10.  Brick  pavements  themselves  yield  little  or  no  mud  or  dust.  11. 
They  are  easily  cleaned.  12.  If  the  joints  are  filled  with  sand,  they 
are  only  slightly  absorbent;  and  if  filled  with  tar  or  cement,  they  are 
absolutely  non-absorbent.  13.  Brick  pavements  have  a  pleasing  appear- 
ance. 1-1.  They  are  very  durable,  particularly  if  the  joints  are  filled 
with  Portland  cement.     15.     They  are  easily  repaired. 


INDEX. 


Page. 

Absorption,    relation    to    porosity    145 

Test     68 

Test,  value  of   , 67 

Theory  of  plasticity   189 

Ackison,    cited    188,  191 

Action    of    ice    22 

Adobe    clays     35 

Analysis    of 14 

Advisability  of  a  Bureau  of  Inspection   72 

Agents  of  decomposition    '  8 

Agents  which  aid  in  the  decomposition  of  rocks   15 

A1203   in   ceramic  mixtures    240 

Albion,   Illinois,   paving  brick   tests    81 

Albion    clays,     analysis     215 

Specific    gravity 139 

Tensile    strength     166,  169 

Albion    Vitrified    Brick    Company    280 

Alexander   county,    Cretaceous   and   Tertiary   in    46 

Devonian    in     45 

Lower  Carboniferous  in    43 

Alton  clays,  analysis  of   215 

Alton  Paving  Brick  Company   280 

Amended  specifications  for  rattler  test    58 

Analyses    of    adobe    clays    14 

Ball    clays    13 

Analyses  of  brick  clays    13 

Clays     284 

Clays    studied 215 

Fire   clays    13 

Flint    clays    13 

Fullers    earth     14 

Glacial    clays    14 

Kaolin  clays    13, 

Loess  clays 14 

Paving  brick   clays    14 

Slip     clays     14 

Stoneware    clays    13 

Terra  cotta  clays   14 

Analyses,   value  of   135,  200 

Apparent   specific    gravity    136,  271 

Areal    distribution   of   geological    formations    44 

Argillo    works    282 

Atchison,    Kansas,    clays,   analyses    216 

Paving   brick   tests    87 

Specific    gravity    139 

Tensile    strength    169 

Atchison    Paving    Brick    Company 284 

B 

B2,    source    of    284 

Back-filling    trenches     291 

Baker,  Ira  O.,.  Construction  and  Care  of  Brick  Pavements 289 

Ball     clays     27 

Analyses     of     13 

Banner    Clay    Company    281 

Barr  Clay  Company    281 

Analyses    of    clays     215 

Specific    gravity    of    clay    139 

Beyer  and  Williams  cited   146,   156,  157,   15S,  170,  183 

Bleininger,   A.,    cited    153,    240,    241,    242,    245,  247 

Bloomington,    Illinois,    early   brick   pavements    289 

Boone    county,    Silurian   in    45 

305 
—20  G 


306 

Index — Continued. 

•^  ^  Page. 

Bourry,    E.,    cited igg 

Brazil,    Indiana,    clay   from    283 

Analysis    of 216 

Firt>    clay,    specific    gravity    ' '    139 

Paving    brick    tests    .....".".   10.") 

Shale,    specific    gravity    1 39 

Tensile   strength    1*6*6*.    168.  169 

Brick    clays ^ 34 

Analyses    of '.......      13 

Brick    for    paving 298 

Brick    pavements 289 

Broken   stone   foundations   for  pavements    296 

Building    brick    clays     274 

Bureau    of    Inspection,    need    of    72 

Burning    qualities    of    clays     219 

Burning    test    pieces 260.  "264- 

C 

Calcium    in    ceramic    mixtures    2-1.4 

Calculated    shrinkage     155 

Calculation    of    fusion    results 267 

Porosity     143 

Calhoun   county,   glacial   deposits   in    43 

Lower    Magnesian    in     41 

St.    Peters   in    42 

Cambrian      41 

Caney,   Kansas,   clays,   analyses  of   216 

Paving   brick    tests 92 

Specific    gravity    ". 139 

Tensile    strength     169 

Cap-an-Gres,   St.   Peters  at   42 

Capital   City  Vitrified  Brick  &  Paving  Co 284 

Carbon    Cliff,    clay    from     282 

Clay,    specific    gravity    139 

Shale,    analysis    216 

Tensile    strength 169 

Carbon    in    clays     ' - 224 

Carbcndale,   glacial  deposit  in   latitude   of   44 

Carboniferous     ' 43 

Care   of   brick   pavements    . : 2S9 

Carhart,    H.    S.,    cited 174 

Cai  ter,    clay   pit    282 

Cement    filler    300 

Ceramics   department,    work   of 64 

.Ceramics,   development  of 133 

Chamberlin,    T    C,    cited    ,.'. 22 

Champaign,    paving   brick    in    36 

Changes     in     sedimentary     rocks     19 

Charleston,     glacial     deposit     near     44 

Charleston,    West    Virginia,    pavements    289 

Chemical   analyses,    value   of    135 

Chemical    balance,    determinations   of   porosity 140 

Specific    gravity    139 

Chemical   changes   in  fusion    250 

Chemical   composition,    effects   on   fusion    239 

Composition    of    granites     4 

Chemical  principles  of  geology  of  clays   1 

Properties    of    clays     •• 200,   211 

Cincinnatian 42 

In    Will    county 45 

Near    Wilmington    45 

Clarke,     F.     W.,     quoted     4 

Classification    of    clays    * 26 

Clay   substances,   percentage   of 14 

Clays,    classification   of 26 

Geology    of    40 

Minor   uses    for    35 

Origin    of    40 

Studied  which  are  suitable  for  use  in  the  manufacture  of  paving  brick   279 

Transported     17 

Clinton,    Indiana,    clays,    analysis    of 216 

Paving    bdick    tests    95 

Tensile    strength 169 

Specific    gravity    139 

Clinton    Paving    Brick    Company    283 

Coal    Measures    43,  45 

Coffeyville    Brick   &    Tile    Company    284 


30" 
Index — Continued. 

Page. 

Coffeyville,    Kansas,    clays,    analysis    of    216 

Clays,    tensile    strength    169 

Paving   block   tests    78 

fie    gravity     139 

Combined    water    in    clays    L52 

Combustion,    incomplete,    effects    of    230 

Comparison   of,   residual  and  transported   clays    ." 17 

T<  s.s     64 

Composition    of    earth's    crust    7 

Conclusions    of    the    values    of    tests     69 

Concrete     foundations      293 

ruction  and  Care  of  Brick  Pavements,  by  Ira  O.  Baker   289 

Construction    of   sub-grade 291 

Cook,    cited     204 

Cook   county.    Silurian   in    45 

Cooling-    test     pieces     265 

Cramer,    E..    cited    207 

Crawfordsville,    Indiana,    clays,   analysis    of    216 

Specific     gravity      139 

Tensile    strength    166.    168,  169 

Paving   brick   tests    113.    114,    115,    116,  282 

Specific    gravity    139 

Cretaceous  and  Tertiary   43,  46 

In   Alexander   county    46 

In   Massac   county    ' 46 

In    Pope    county    .  .  , 46 

In    Pulaski    county    46 

Cross-breaking    test    62 

Value    of     6^7 

Crushing    test    62 

Value    of     „. 67 

Culling   of    brick    71,   72 

Cushion   of   sand   in   pavements    : 297 

Cushman,  cited   150,   188,   195,  196 


Daubree,    cited    195 

Danville  Brick  Company,  specific  gravity  of  clays    139 

Danville   Brick  and   Tile   Company    282 

Tests  on  paving  brick  from   100,   130,  131 

Danville,    clay   from    281 

Clays,   analvsis   of    215 

Tensile   strength   of    166,    168,  169 

Lower   Carboniferous  near    43 

Tests  of  brick  from   130 

Data  from  fusion  trials    262,  267 

Decatur,   glacial   deposit   near    44 

Decomposition    of    granitoid    rocks    8 

Rocks,   agents   which   aid  in    15 

Sedimentary    rocks     21 

Decrease   in   porosity   with   heat    202,  268 

Definition    of   porosity    140 

Oxidation      22^ 

Deflocculation    in    clays    191 

Dehydration    in    burning    i 220 

Deposition,    final    of   clays    18 

DeKalb  county,   Silurian  in    45 

Ice   as   an   agent   of    23 

Deposits  of  residual  clays    16 

Formation    of 21 

Depth  of  deposits  of  residual  clays    16 

Determination    of,    porosity    140 

Specific     gravity     . 136 

Development  of  plasticity,   by  water    '. 189 

In    clays    195 

Devonian    42,  45 

In  Alexander  county    45 

In    Union    county    45 

Near   Jonesboro    45 

Near   Rock   Island    45 

On    Illinois    river    45 

De  Wolf.  Purdy  and,  cited   202,   206,  218 

Diamond,    Missouri,    clay  from    283 

Diamond  paving  brick,  tests  of   T07 

Differentiation   between  clays    " 259 


308 
Index — Continued. 

Page. 

Discussion  of  tests    64 

Distribution   of   carbon,    effects   of    \ 227 

Dixon,   St.   Peters  near   42 

Drainage    of   road    ways    291 

Drain-tile    clays    34 

Drying,   shrinkage  in    154 

Drying   test   pieces    264 

DuPage  county,   Silurian  in    45 

Dupiers   and   Son,    clay 282 


Earth's  crust,    original   composition    7 

Eckel,    E    C,    cited    243 

Edwardsville,   clay  from    281 

Clays    analyses   of    215 

Paving  brick   tests    103 

Specific    gravity    139 

Tensile    strength    169 

Effect  of  grinding  on  tensile  strength    166 

Rattler    test    67 

Traffic    on    paving   brick    69- 

Emergence    of    sedimentary   rocks    19 

England,  brick  pavements  in   289 

Eutectic   mixtures    241 

Erosin,  action  of  ice  in    22 

Of    rocks     16 

Errors  in  determining  porosity    144 

Excess    water    and    shrinkage    161 

In   pores    156 


F1(    source    of    , 282 

Factors  affecting  fusion  of  clays   239 

False    specific    gravity    271 

Ferrous   carbonate   in   clays    224 

Ferrous   sulphide  in  clays    226 

Fillers  for  brick  paving   300 

Filling  joints  in  pavements    300 

Final  trials  for  fusion   264 

Fineness    of   grain    149 

Effect   in   burning    228 

Of  clays  studied   286 

Tensile   strength,   and    170 

"Volume    shrinkage,    and    162 

Fire  clays    28,    270,  273 

Analyses   of    13,  273 

Firing  test  pieces 264,  266 

Flint    clays     : 31 

Analysis    of    13 

Flocculation    in    clays 194 

Fluxes,    operation   of  in   clays    207 

Ford   county,    Ordovician   area   in    44 

Formation  of,   residual  clays    1Q 

Sedimentary  rock   and   clays    16 

Shales 19 

Silicates    in    clays    2 

Formulae  for  fineness  of  grain   150 

Foundations  for  pavements    292 

Fox,  H.   B.,  quoted    163,   182,  219 

Fox   river  .  valley,    St.    Peters    in    42 

Fullers   earth    35 

Analyses    of    14 

Furnace  for  testing  work   261 

Fusion      232 

And    vitrifcation,    distinction   between    38 

Period  of  clays 232 

Trials     259 

G 

G2,   source   of    284 

Galena  clays,  analysis  of   : 216 

Specific    gravity    139 

Tensile  strength    169 


Index — Continued . 

Page. 

Galena-Trenton     42 

Galesburg,  clay  from    281 

Galesburg  clays,   analyses  of   215 

Specific    gravity    139 

Tensiie    strength    169 

Galesburg,  Illinois,  paving  brick  tests   117,  118 

General  conclusions  regarding  fusion    277 

Geological  distribution  of  paving  brick  material  in  Illinois    36 

Geological  formation,  areal  distribution  of   44 

Geological   history  of  Illinois 40 

Geology  of  clays,   by  C.   W.   Rolfe    1,  40 

Georgia  Geological  Survey,   cited   187 

Gilbert,  G.  K.,  cited   20 

Glacial    clays,    analyses    of    14 

Characteristics     of     24 

Glacial    deposits   in    Calhoun    county    43 

Near   Carbondale    44 

Charleston     44 

Decatur     44 

Harvard     44 

Peoria    44 

Princeton     44 

Rochelle    44 

Shelbyville     44 

Woodstock     44 

Glass  in  fused  brick   254 

Glen    Carbon   clays    280 

Granitoid  rocks,   composition  of   i 

Decomposition     8 

Gravel  foundations  for  pavements    295 

Gravity  in  plasticity   '. 189 

Green  brick,  porosity  of   146 

Tests   of 137 

Grimsley,   G.  P.,   cited    183 

Grout,  F.  P.,  cited 175,  177,  178,  180,  186,  197,  219 

Grout    filler    300 

Gumbo    clays    , , 34 

H 

H2,   source  of   284 

Hia,  H17,  H18,  H20,  H21,  H23,  source  of 282 

Hardness    of    paving    brick    49 

Harrington,    E.    P.,    quoted    54 

Harvard,   glacial   deposit  near 44 

Hatt,   W.   K.,    tests  by    57 

Hegley,  J.  L.,   tests  by a 57 

High    grade,    clays    26 

Paving  brick,   qualities  for    48 

Paving  brick,  qualities  of  and  tests  used  in  determining  them   47 

Hintze,    cited    255 

History  of  brick  pavements    289 

Paving   bricks    133 

Hoffman    and    Desmond,    cited    218 

Holland,   brick  pavements  in    289 

Paving  bricks   in    133 

Hopewood,    experiments    of    222 

Hydraulic   Press   Brick    Company    280 

Hydraulic,   St.  Louis,  Missouri,  paving  brick  tests    . . . , 104 

Hygroscopic    water    and    shrinkage    161 

In    clays    studied    ■ 286 

I 

I2,    source    of    284 

Ice,    action    of 22 

Ice  as  an  agent  of  deposition   23 

Eroding   and    transporting   agent    22 

Illinois  clays,  analyses  of  215,  216,  284 

Specific    gravity    of     139 

Tests     of 177 

Illinois,  geological  history  of 40 

Illinois   Geological   Survey,   cited    202,    206,  218 


310 
In  dex — C  onti  nued . 

T1.  .  _  .  Page. 
Illinois   river.   Devonian   on    45 

Silurian  at  mouth  of 45 

Imbibing-   power    of    clays [['/   145 

Imperial  clays,   analysis  of 216 

Paving-    block,    tests    of ........  .93,94 

Importance  of  slow  vitrification    '.'.'.'..   259 

Impurities   occurring   in   clays    ...........'.     11 

Incomplete    combustion,    effects    of 230 

Indiana  block,  paving  brick  tests   '. . .  .105,  129 

Indiana  clays,  analyses  cf    .216*  285 

Specific    gravity    of    '.'. . . .'  139 

Tensile   strength   of    • 166,'  16*8,  169 

Tests   of    177 

Indiana  Paving  Brick  &   Block   Company    283 

Inspection    of    paving 299 

Paving    brick     70,  71 

Iowa  clays,   porosity    146,  158 

Tests    of     177 

Iowa  Geological  Survey,  cited   146,  156,  157,  158,  177,  182 

Iroquois  county,    Ordovician  area  in    44 

Silurian    in    45 

J 

Jackson  and  Richardson,   cited   195 

Johnson,    cited    57,    145,  191 

Jones,    Gomer,    tests   by    57 

Jonesboro,  Devonian  near   45 

K 

Ki,  Ko,  Ko„   K4,  source  of   28a 

K5,    KQ,    K7,    source    of    281 

K8,   Ka,    source   of    2 282 

Ku,  Kio,   K13,   sou rce  of   283 

Ku,   K15,   source  of   281 

Kane   county,    Silurian   in    45^ 

Kankakee    county,    Ordovician   area    in    44 

Silurian    in    45 

Kansas  City  clays,    analyses   of   216 

Diamond     paving     brick     tests     107 

Hydraulic   Pressed   Brick  Company    283 

Missouri,   clays,   specific  gravity   139 

Tensile^  strength   169 

Kansas   clays,   analyses   of   285,  216 

Specific    gravity    139 

Tensile     strength     169 

Tests    of     178 

Kaolin    26 

Clays,  analyses  of   13 

Kemp,    cited     4 

Kennedy    curves     53 

Krehbiel  device  for  groving   164 

L 

L2,   source   of    284 

Laboratory  of  Applied  Mechanics,  tests  of  74 

Ladd,    G.    A.,    cited    187 

Lake   county,    Silurian   in    45 

Laminations   in   paving   brick    .  „ 50 

LaSalle   at    close    of    Silurian 42 

Clay,    specific   gravity    139 

Clays,    analyses    of     216 

County,   Lower  Magnesian  in    ; .     41 

LaSalle,  St.  Peters  near  42 

Lawrence    clays    216 

Lawrence,    Kansas,    clays,    specific   gravity    139 

Tensile     strength     !■ 169 

Lawrence,  Kansas,   Paving  brick  tests   108 

Lawrence  Vitrified  Brick  &  Tile  Company   284 

Limiting  values  for  the  requirements  for  brick   70 

Limits  for  the  modulus  of  rupture   70 

Linear    shrinkage     154 

Of   clays    studied 286 

Lirchvig,    cited 211 


311 
Index — Continued. 

Page. 

Litchfield,    Lower    Carboniferous   at    • 43 

Loess,     clays     35 

Analyses    of    14- 

Origin    of     -5 

Loss  by  the  X.   B.   M.  A.   standard  rattler  test 70 

Loss     in     dehydration     221 

1  .i >\v    grade    clays    26 

Lower  Carboniferous    43,  45 

At    Danville     43 

At    Litchfield    43 

At    Xew    Boston     „ 45 

In   Alexander  county    43 

In    Mercer  county    43,45 

In    Ozark   ridge    43 

1  icwer     Magnesian     41 

In   Calhoun    county    41 

In   LaSalle   county    41 

In    Ogle    county    41 

Xear    Utica    41 

M 

Mc  Henry   county,    Silurian   in    45 

Macadam   foundations   for   pavements    296 

Magnesia    in   ceramic    mixtures    243 

Maquoketa 42 

Shale     282 

Marking  test  pieces 264 

Marston,     A.,     tests    by     57 

Massac   county,    Cretaceous   and   Tertiary   in    46 

Meade,  R.  K.,   cited    ' 222,  238 

Measurement   of  plasticity 197 

Shrinkage     154 

Mellor,   J.  W.,  cited 195,   213,   222,  238 

Mellor's    fusion    curve 214 

Mercer   county,    Lower    Carboniferous    43,  45 

Merits    of    brick    pavements ; 303 

Metamorphism    of    sedimentary    rocks 20 

Methods    of    determining   porosity    140 

Specific    gravity    136 

Methods  of  measuring  plasticity    197 

Testing   tensile    strength    163 

Metropolitan    clays,    analyses    of    216 

Paving    brick,    tests    of    93,94 

Microscopic     studies-    of     brick     247,  254 

Mineral     composition     of    granites     4 

Mineralogical   composition   and    fusion    233 

Of     clays     203 

Minor  uses  for  clays  35 

Mississippian      43,  45 

Shales     282 

Missouri   clays,   analyses   of    216,  285 

Specific    gravity    139 

Tensile    strength     169 

Moberly  Brick,   Tile  &  Earthenware  Company 283 

Moberly,   Missouri,   clays,   analyses  of   216 

Specific    gravity 139 

Tensile    strength     169 

Moberly,    Missouri,    paving    brick    tests     110 

Modulus    of    plasticity     199 

Rupture     70 

Moisture   in   oxidation    230 

Molding  test  pieces   264 

Molecular    attraction    in    clays    ' 189 

Theory  of  plasticity 173 

Moore,  purdy  and,  cited   233 

N 

N.  B.  M.  A.,  paving  brick  committee  57 

Rattier    test     73 

Losses     70 

Tests    53,   58,  298 

Natural   plasticity    of    clays    195 

Nature   of  dehydration    221 

Nauss,    cited     243 

Nelsonville   Brick   Company    283 


312 

Index — C  ontinued . 

Nelsonville,   Ohio,   paving  brick  tests    HO 

Specific   gravity "  139 

Tensile    strength '  169 

New  Boston,   Lower  Carboniferous   at 45 

New  Jersey  Geological   Survey,   cited   . . . . "  204 

Niagaran 42 

Number   1    fire    clays 270 

Number  2  and  3  fire  clays 2T> 

Ogden,    cited '  239  * 

Ogle    county,    Lower   Magnesian   in    .........'*  41 

Ohio    clays,    analyses    of 216  285 

Specific    gravity    ....... .'  139 

Tensile    strength    .....'.'.  169 

Tests    of ' '      ' '  177 

Old  N.  B.  M.  A.  tests  . ... .".'.'.".'.'.'.'.'.'.'. !  55 

Ordovician     41   44 

In    Ford    county    ..............'  44 

Iroquois    county 44 

Kankakee    county    .......  44 

Will    county . . .  .  44 

Oregon,   St.   Peters  north  of   .' \  42 

Orton,   Edward,   Jr.,   cited    53,    185,    207,  221 

Tests    by    ' .'  57 

Ottawa,   St.  Peters  near  42 

Oxidation    in    burning    222 

Oxides    in   ceramis    mixtures    247 

Ozark  ridge,  Lower  Carboniferous   in ~43 


Pavements     of    brick 289 

Faving    brick    clay,    analyses    of    14 

Conditions    essential    in     38 

What  is  a    36 

Studied     . . 274,   279 

Paving    brick    in    Champaign    36 

Urbana     36 

Paving  brick  material,   geological  distribution  of,   in  Illinois    36 

Paving    brick    tests     .' 

122,  123,  124,  125,  126,  127,  128,  118,  119,  120,  121,  117,  113,  114,  115,  116,  129,  130,  131 

Pectoidal    theory   of   plasticity    187 

Peeble's   Block,   Portsmouth,   Ohio,    paving  brick   tests    Ill 

Pennsylvanian 43,  45 

Peoria,    clay    from     282 

Clay,    tensile    strength    169 

Peoria  clays,    analyses   of    216 

Specific    gravity    139 

Peoria,    glacial    deposit    near    44 

Percentage    of   clay    substances    14 

Physical  properties  of  clays    136,  217 

Physical  tests  of  clays  studied   286 

Pierce,   C.   I-L,   tests  by 74 

Pittsburg,    Kansas,   clays,    analyses   of    216 

Specific    gravity    139 

Tensile    strength    169 

Fittsburg,   Kansas,   paving  brick  tests 112 

Plasticity     173 

Modulus     199 

Pleistocene 43 

Plotting  fusion   results    267 

Pope    county,    Cretaceous    and    Tertiary    in 46 

Fore   space   in   rocks 8 

Porosity    . 140 

Changes    in    fusion     . . . 256 

Decrease  with  heat   262,  268 

Porosity  of  clays  studied    286 

Porosity,  relation  to  absorption    145 

Shrinkage 156 

Portsmouth,   Ohio,   clays  analysis   of    216 

(Specific    gravity 139 

Tensile  strength 169 

Portsmouth,  Ohio,  paving  brick  tests    110 

Portsmouth  Paving  Brick  Company   ; 283 

Boston  Block,  paving  brick  tests  on 113,  114,  115,  116 

Poston   Paving   Brick    Company 282 

Potsdam    time 41 

Pottery  clays    32 


313 

Index — Continued. 

Page. 

Preliminary  fusion   trials    259 

Frinceton,   glacial   deposit   near    44 

Processes    of    decomposition 8 

Pulaski   county,    Cretaceous  and   Tertiary   in    46 

Punkness    in   brick    242 

Purdy,  R.   C,   cit^ed   240 

Purdy  and  DeWolf ,   cited   202,   206,  218 

Purdy   and   Moore,    cited    233 

Purdy,  Ross  C,  Pyro-Physical  and  Chemical  Properties  of  Paving  Brick  Clays  217 

Qualities  of  Clays  Suitable  for  making  Paving  Brick   133 

Tests    of 74 

Purington,   D.  V.,   tests  by    57 

I'urington  Block,   paving  brick  tests  on    117,  118 

Purington  Paving  Brick  Company 281 

Pycnometer    determinations     138 

Fyro-Chemical   properties    of   clays    217 

Pyro-Physical  and  Chemical  Properties  of  Paving  Brick  clay,  by  R.  C.  Purdy..   217 


Qualities  of  Clays,   Suitable  for  Making  Paving  Brick,  by  Ross  C.   Purdy 133 

Qualities  of  high-grade  paving  brick  and  tests  used  in  determining  them   47 

Quality  of  paving  brick   57 


Ri,   R2,  R3,  R4,   source  of   283 

Rate    of   fusion    233 

Vitrification     263 

Rational  analysis  of  clays  studied   216,  285 

Rational    analyses,     value     of .' 277 

Rattler    losses     70 

Rattler   loss,    proportional    '. 77 

Rattler    test    '. 52 

Effect     of     67 

Results    of     75 

Raw  clay  porosity  determinations   146 

Raw  qualities   of  clays    219 

Real   specific  gravity 136 

Re-erosin    of   clays    18 

Regularity  of  paving  brick   51 

Relation  of  Chemical  and  Physical  constitution  to  behavior  in  fusion   239 

Requirements  for  paving  brick   69,  70 

Residual    clays    10 

Comparison    of 17 

Depth  of  deposits  of 16 

Formation  of  deposits  of   21 

Results  of  fusion  tests    270 

Richardson,   Jackson  and,   cited    195 

Richter,     cited     207 

Richter    law    of    fluxes    211 

Rieke,    cited    , 213,  243 

Ries,   H..   cited    170,   188,  197 

Road   Laboratory    of   the    Civil    Engineering   Department    ot    the    University    of 

Illinois,    tests    73 

Rochelle,   glacial  deposit  near   44 

Rock  Island,  Devonian  near  45 

Kock  river  valley,   St.    Peters   in 42 

Rocks,  agents  which  aid  in  the  decomposition  of  15 

Changes  in  sedimentary   19 

Erosion    of 16 

Transportation    of    16 

Rodden,    clay    from 282 

Rolfe,    C.    W.,    cited    204 

Geological  Distribution  of  Paving  brick  material  in  Illinois    36 

Geology    of   Clays    1 

Rolling    Davements 289 

Sub-grade     292 

Roth,    cited    250 

RuDture.   modulus   of    • : 70 


Sl    S2,    source    of    283 

St.   Louis   clays,   analyses   of    216 

Specific    gravity    139 

Tensile    strength     169 


314 
Index — Continued. 

^  Page. 

St.    Peters    I  _> 

At   Cap-au-Gres 42 

In   Calhoun   county    "  42 

In    Fox    river   valley ,  42 

In   Rock   river  valley    \  \\  42 

Near    Dixon 42 

Near    LaSalle     42 

Near    Ottawa    !!!!!!  42 

North  of  Oregon    \\  42 

Sand    cushion    in    pavements 297 

Sand     filler     300 

Saturation  of  test  pieces    . .  266 

Savannah,    clay    near 282 

Savanna    clays,    analysis   of    216 

Specific    gravity    139 

Tensile    strength     169 

Schuber's    table    of   absorption 145 

Sedimentary    clays,    formation    of    16 

Rocks,    changes    in    19 

Decomposition    of     21 

Formation   of 16 

Metamorphism    of ....    20 

Segar,  H.,  cited   200,  212 

Segers    Volumeter    136 

Setting  paving  brick 299 

Setting    test    pieces     259 

Shales,  formation  of   .- .- 19 

Shelbyville,    glacial   deposit   near 44 

Shrinkage 161 

In    drying 154 

Shrinkage    of    clays    studied    286 

Silica  and   silicic  acid  in  clays   1 

Silica   in    ceramic    mixtures    241 

Silicates,     formation    of     2 

Silurian     42,45 

At   mouth   of  Illinois   river    45 

East   of    Thebes    45 

In    Boone    county    45 

In    Cook    county 45 

In   DeKalb   county    45 

In  Dupage  county   45 

In   Iroquois    county    45 

In   Kane   county    45 

In   Kankakee   county    45 

In   Lake    county    45 

In    McHenry    county 45 

In    Will    county    45 

LaSalle  at  close  of 42 

Singer,    cited     225 

Size  of  grain,   affecting  fusion   235,  245 

And    plasticity     179 

Slip   clays,    analyses  of    14 

Slip    process    versus "  wedging    165 

Smithsonian    Institute,    cited 192 

Specific    gravity    271 

Changes  in  fusion    256 

Of   clays 136 

Of    clays    studied    286 

Test    64 

Springfield    clays,    analyses    of    215 

Specific    gravity    139 

Tensile    strength    169 

Springfield,  Illinois,  paving  brick  tests  ,  118,  119,  120,  121 

Springfield   Paving  Brick   Company 280 

Stable    iron    compounds    in    clay 228 

Standard  tests  for  paving  brick    55,  58 

Sterling,     clay    from     282 

Sterling  clays,   analyses  of 216 

Specific    gravity    139 

Tensile    strength    169 

Stoneward  clays,   analyses   of    13 

Streator,    clay   from    281 

Streator   clays  analyses   of    215 

Specific    gravity    139 

Tensile    strength    169 

Streator  Paving  Brick  Company    281 

Paving    brick    tests     122 

Streator,    paving    >->rick    tests     88,  122 


315 
Index — Continued. 

Page. 

Strength    of    concrete    foundations     2*94 

Paving    brick     49 

Structure    of    clay    ware    229 

Paving   bi  Ick    50 

Ware    affecting    fusion     238 

Studies  of  paving  brick  clays    134 

Stull.     cited     183 

Subgrade    of    pavements    291 

Substances  affected  by  oxidation   223 

Substances,    percentage    of    clay    14 

Surface    pressure    in    clays 190 

Surface   tension   in   clays    190 


Talbot,    A.    N.,    cited    36,74 

Qualities  of  High  Grade  Paving  Brick  and  Tests  used  in  Determining  them     47 

Tests    by    57,  74 

Talbot-Jones    rattler    57,  59 

Tar   filler    300 

Technograph,     cited     52,56 

Temperature    in    oxidation     230 

Tensile    strength     163 

And   fineness   of  grain 170 

And   volume   shrinkage    172 

Of  clays  studied   286 

Terra   cotta    clays    33 

Analysis    of     14 

Terre  Haute  Block,  paving  brick  tests    122,    123,    124,  125 

Terre  Haute,  Indiana,  clays,  analyses  of  216 

Specific    gravity    139 

Tensile    strength    166,    168,  169 

Paving  brick  tests  on  clays  from   122,   123,  124,  125 

Terre  Haute  Vitrified  Brick   Company    283 

Tertiary 43 

Test    cones    259 

Testing   paving    brick 298 

Trial    pieces    260 

Tests  of  clays  studied   286 

Tests   of  green   brick    137 

Paving   brick    51,  73 

Tensile    strength    163,  169 

Tests,    tables    of    66 

Tests  used  in  determining  qualities  of  high  grade  paving  bricks   47 

Thebes,   Silurian  east  of 45 

Theories    of    plasticity    173 

Thermo-chemical   changes   in    fusion-   250 

Reactions      233 

Topeka   clays,    analyses    of 216 

Topeka,    Kansas,   clay  from    284 

Specific    gravity    139 

Tensile    strength 169 

Topeka,  Kansas,  paving  brick  test   126 

Toughness    of    paving   brick    49 

Traffic   on  brick  paving   69 

Transportation,   action  of  ice   on    22 

Of   clays    18 

Of    rocks     16 

Transported    clays     17 

Comparison  of   17 

U 

Ultimate  analyses,  value  of    277 

Composition    of    clays    206 

Under  drainage   of   pavements    291 

Uniformity  in  paving  bricks   50 

Union  county,  Devonian  in   45 

U.   S.  Department  of  Agriculture,  cited   184,  189,  191,  193,   194,  196 

University   of   Illinois,    acknowledgments    to    74 

Urbana,    pacing    brick    in    36 

Utica,   Lower  Magnesian   near    41 


31G 

Index — Concluded. 
v 

Page. 

Value   of  absorption   test    , 67 

Cross    breaking    test 67 

Crushing-    test 67 

Van   Hise,    cited 8 

Veedersburg,    Indiana,    clays 282 

Analyses     of     216 

Specific     gravity     139 

Tensile    strength 166,  169 

Veedersburg  paving  brick,  tests  on   126,  127,  128,  129'  130 

Vitrifaction   and   fusion,   distinction   between    3,  8 

Vitrification     259 

Rate     263 

What   is 37 

Vitrifying    clays    32 

Volatile   matter   affecting   fusion    237 

Volume    changes    in    fusion    256 

Volume    shrinkage     154 

And    fineness    of   grain 162 

Of  clays  studied   286 

Relations    to    water    of   plasticity 156 

Tensile    strength    and    172 

Volumeter    136 

Determination    of    porosity    141 

Wabash    Clay    Company    282 

Paving  brick  tests 126,   127,   129,   128,  130 

Tests    of    brick 129 

Water    and    plasticity     189 

Water  of  plasticity  of  clays  studied    286 

Relations   to   volume    shrinkage    156 

Watts,    cited 243 

Way,    T.,    cited    188 

Weathering   of  paving  brick    50 

Wedging    test    clays     264 

Versus    slip    process     165 

Wegemann,    C.   H.,   Notes   on   Microstructure   of  certain   Paving  Brick  Clays  at 

Various   Stages   of  Fusion    254 

Quoted     247,  254 

Weller,    Stuart,    cited 40 

West  Virginia,    clay  analyses    180 

Geological  Survey,  cited   177,   178,   180,  197 

Western    Brick    Company    281 

Clays,    analysis    of    •• 215 

Clays,    specific   gravity 139 

Clays,    tensile    strength    166,    168,  169 

Western  pavers,   Danville,   Illinois,   tests  on    130,  131 

Western  Paving  Brick  Company,   tests  of  brick    130 

Wheeler,  H.  A.,   cited   174,   185,  186 

Tests    by    : 57 

Whitney,    Milton,    cited    184,    189,  191 

Whittemore,    H.   L..,    tests   of    74 

Width  of  brick  pavements    290 

Will    county,    Cincinnatian    in    45 

Ordovician     area    in     *  44 

Silurian    in    45 

Williams,    cited    170,  177 

Wilmington,    Cincinnatian    near      , 45 

Woodstock,   glacial   deposit   near    44 

Worcester,  cited 242 

Worthen,     cited     43 


Zschokke,    cited    •• • 1 9" 


LIST   OF   PUBLICATIONS. 


A  portion  of  each  edition  of  the  Bulletins  of  the  State  Geological  Survey  is 
set  aside  for  gratuitous  distribution  by  the  Survey  and  by  the  Secretary  of 
State.  To  meet  the  wants  of  libraries  and  individuals  not  reached  in  this 
first  distribution,  500  copies  are  in  each  case  reserved  for  sale  at  cost,  includ- 
ing postage.  The  reports  may  be  obtained  upon  application  to  the  State 
Geological  Survey,  Urbana,  Illinois,  and  checks  and  money  orders  should 
be  made  payable  to  H.  Foster  Bain,  Director,  Urbana. 

The  list  of  publications  is  as  follows: 

Bulletin  1.  The  Geological  Map  of  Illinois:  by  Stuart  Weller.  Including 
a  folded,  colored  geological  map  of  the  State  on  the  scale  of  12  miles  to  the 
inch,  with  descriptive  text  of  26  pages.  Gratuitous  edition  exhausted.  Sale 
price  45  cents. 

Bulletin  2.  The  Petroleum  Industry  of  Southeastern  Illinois:  by  W.  S. 
Blatchley.  Preliminary  report  descriptive  of  condition  up  to  May  10th,  1906. 
109  pages.    Gratuitous  edition  exhausted.     Sale  price  25  cents. 

Bulletin  3.  Composition  and  Character  of  Illinois  Coals:  by  S.  W.  Parr. 
With  chapters  on  the  Distribution  of  the  Coal  Beds  of  the  State,  by  A.  Be- 
ment,  and  Tests  of  Illinois  Coals  under  Steam  Boilers,  by  L.  P.  Breckenridge. 
A  preliminary  report  of  86  pages.  Gratuitous  edition  exhausted.  Sale  price 
25  cents. 

Bulletin  4.  Year  Book  of  1906,  by  H.  Foster  Bain,  director,  and  others. 
Includes  papers  on  the  topographic  survey,  on  Illinois  fire  clays,  on  lime- 
stones for  fertilizers,  on  silica  deposits,  on  coal,  and  on  regions  near  East 
St.  Louis,  Springfield  and  in  Southern  Calhoun  County.  260  pages.  Gratui- 
tous edition  exhausted.     Sale  price  35  cents. 

Bulletin  5.  Water  Resources  of  the  East  St.  Louis  District:  by  Isaiah 
Bowman,  assisted  by  Chester  Albert  Reeds.  Including  a  discussion  of  the 
topographic,  geologic  and  economic  conditions  controlling  the  supply  of  water 
for  municipal  and  industrial  purposes,  with  map  and  numerous  well  records 
and  analyses.    Postage  6  cents. 

Bulletin  6.  The  Geological  Map  of  Illinois:  by  Stuart  Weller.  Second 
edition.  Including  a  folded  colored  geological  map  of  the  State  on  the  scale 
of  12  miles  to  the  inch,  with  descriptive  text  of  32  pages.  It  includes  correc- 
tions and  additions  to  the  former  map  and  text  and  shows  locations  of  mines 
where  coal,  lead,  zinc  and  flourspar  are  produced.  The  great  oil  fields  of 
southeastern  Illinois  are  also  outlined.  Gratuitous  edition  exhausted.  Sale 
price  45  cents. 

Bulletin  7.  Physical  Geography  of  the  Evanston-Waukegan  Region:  by 
Wallace  W.  Atwood  and  James  Walter  Goldthwait.  Forming  the  first  of 
the  educational  bulletins  of  the  survey  and  designed  especially  to  meet  the 
needs  of  teachers  in  the  public  schools.  102  pages.  Gratitous  edition  ex- 
hausted.    Sale  price  25  cents. 

Bulletin  8.  Year  Book  for  1907:  by  H.  Foster  Bain,  director,  and  others. 
Including  administrative  report;  papers  on  the  general  geology  and  mineral 
production  of  the  State;  a  directory  of  the  clay  industries;  reports  on  stream 
improvement,  land  reclamation  and  topographic  mapping;  on  field  and  labor- 
atory studies  of  coal,  cement  materials,  oil,  gas,  lead,  zinc  and  silica.  393 
pages.     Gratitous  edition  exhausted.     Price  30  cents. 

Bulletin  9.  Paving  Brick  and  Paving  Brick  Clays  of  Illinois:  by  C.  W. 
Rolfe,  R.  C.  Purdy,  A.  N.  Talbot  and  I.  O.  Baker.  Including  a  discussion 
of  the  geology  of  clays,  the  qualities  of  high  grade  paving  brick,  the  prop- 
erties of  paving  brick  clays,  tests  and  methods  of  testing,  and  the  construc- 
tion and  care  of  brick  pavements.     315  pages.     Postage  13  cents. 

Circular  No.  1.  The  Mineral  Production  of  Illinois  in  1905.  Pamphlet, 
14  pages,  postage  2  cents. 

Circular  No.  2.  The  Mineral  Production  of  Illinois  in  1906.  Pamphlet, 
16  pages,  postage  2  cents. 

Circular  No.  3.  Statistics  of  Illinois  Oil  Production.  1907.  Folder,  2 
pages  postage  1  cent. 

Circular  No.  Jf.  The  Mineral  Production  of  Illinois  in  1907.  Pamphlet, 
16  pages,  postage  2  cents. 


ERRATA. 


p. 

181. 

p. 

181. 

p. 

190. 

p. 

199. 

p.   141.     Formula   in  third  paragraph  should  read 

100    [(W— D)  +  S  I  =/0  p0r0Sity  where  W  is  the  saturated  weight  of  the  briquette; 

D  ,the  dry  weight  of  the  briquett;  S,  the  density  of  the  oil,  V,   the  volume  of  the 

briquette, 
p.   175.     The  expression  which  is  assumed  to  present  the  relative  value  of  the  sev- 
eral factors  controlling  drying  behavior  of  clays  should  read. 
S3  T 
i    y  -|  3       =M  (drying  modulus)  where  S  is  the  surface  factor  representing   fine- 

— —        E         ness  of  grain;  „T,  the  tensil  strength;  V,   volume  shrinkage  in   per- 
*-  1UU  ->  cents  and  E,  the  excess  water. 

Second  paragraph.     Instead  of  table  XVI  it  should  read  table  XVIII. 
In    table   XX   data   in   the    last   column   are   parts   of    the    "Weight   Ratio." 

The    subheading    "Weight    Ratio"    should    have    been    extended    so    as    to 

cover  all  of  the  last,  three  columns. 
Second   paragraph   next   to   the   last  iine4  in   place   of  the  word   "radically" 

it  should  read  "raidialy." 
The    development    and    final    expression    of    the    plasticity,    modulus    should 

be  as  follows: — 

For   the  decrease   in  area  of   cross   section   due   to   the  initial  stretch  we 

have 

1.93        1.93+1.92a— 1.93       1.92a       ,  ,.„..,  .    t .    ...  ,     .    ..  . 

1.92  =  --R —  = Lrm '  =  ^—rn~  where     a    is  the  amount  of  initial  stretch. 

1.9— a  1.9+a  1.9+a 

For  the  decrease  in  cross  section  due  only  to  the  final  stretch  we  have 

1.93  1.93  1.93b 

or 


1.9+a        1.9+a+b       1.92+3.8a+1.9b+a2 +ab 
A   measure   of   the   tension    which   is   holding   the   grains    together   is   as- 
sumed to  be  directly  as  the  load  and  inversiy  as  the  product  of  the  de- 
crease in  cross  section  due  to  the  initial  and  final  stretch.     On  performing 
these   indicated  operations  we  have  resulting 
T    f  6. 859+10, 83a +B.61b+5.7a2+3.8ab+a3+a2bl  _  M 
^  I  2+76ab  j  ~ 

p.  210.    Fig.  21  should  be  described  as  "Diagram  showing  operations  of  riuxes  on  A1203+ 
2Si02+^Sio2  using  fractions  of  their  molecular  weights." 

p    219.     The  page  citations   left  blank  should  read  for   the   Grout   reference   p   181- 
186  inclusive  and  for  the  Fox  reference  p.  186. 


LIBRARY  CATALOGUE  SLIPS. 


[Mount  each  slip  on  a  separate  card,  placing-  the  subject  at  the  top  of  the 
second  slip.  The  name  of  the  series  should  not  be  repeated  on  the  Series  card, 
but  the  additional  numbers  should  be  added,  as  received,  to  the  first  entry.] 


Author. 


Rolfe,  C.  W.,  and  others. 

Paving  Brick  and  Paving  Brick  Clays  of  Illinois. 
Urbana,  University  of  Illinois,  1908. 

(33  fig.,  3  pi.,  316  pp.)    State  Geological  Survey.    Bulletin  No.  9. 


Subject. 


C.  W.  Rolfe  and  others. 

Paving  Brick  and  Paving  Brick  Clays  of  Illinois. 
Urbana,  University  of  Illinois,  1908. 

(33  fig.,  3  pi.,  316  pp.)    State  Geological  Survey.    Bulletin  No.  9. 


State  Geological  Survey. 
Series.  Bulletins. 

No.  9.     C.  W.  Rolfe  and  others. 

Paving  Brick  and  Paving  Brick  Clays  of' Illinois. 


